Which Battery to Buy?
 

At the offseason events 1885 attended in the last two weeks, we struggled to maintain proper charge on some of our batteries. I'm not sure who/what/why or even how we got the batteries we have, but they're a mixed bag of some of the FRC legal batteries from 2014.

Problem is, not all of the brand new batteries hold proper charge for an entire match. The Sigma battery had the worst "life" - as in, it would start at 13.5V and always come back at < 10V according to the Battery Beak.

I found a comparison of specs for batteries related to the FRC-legal batteries, which led me to the fact that I don't know which specs actually matter for our use case:
http://www.atbatt.com/sealed-lead-ac...s-12180-nb.asp

Which FRC-legal models (other than the Enersys) worked well for teams this past year?

Re: Which Battery to Buy?
 

There is some information here on the topic

It stays on topic about as well as most CD threads do, but has a few tidbits of useful information.

One addition about he Werkers, they get hot when charging and never seem to reach a full charge. Not scary hot, but noticeably warm to the touch. I would not reccomend them for use by any team. We have had nothing but good luck with the Enersys and will continue to use them.

Re: Which Battery to Buy?
 

Sigma, National Battery (all black), Enersys, MK all worked well.

We had a couple of Sigmas and National Battery that had questionable cells, so we reserved them for non-competition. This is likely what you're experiencing too. For the most part, the Sigmas have been good. I did notice that the Sigma batteries we bought in 2012 are different than the Sigmas today in terms of color scheme and price (almost $10-13 more each!).

How long have the batteries been sitting? SLA needs to be charged to 100% every 6-9 weeks or so when in storage if I recall correctly (pinging adciv).

Re: Which Battery to Buy?
 

6 or 9 what

Re: Which Battery to Buy?
 

I would assume months?

Re: Which Battery to Buy?
 

Our Werkers lasted through a match just fine, but had odd charging right from the store. We use a ten battery battery tender unit and they never reached full charge on that unit. Tried a higher end Optima charger/maintainer and had the same result. The KOP charger never passed 75%. But the batteries got noticeably warm to the touch. Voltage read fine (13.4-13.6V) at full charge, but using a automotive load tester, we only got readings of 140-165 CCA. The Enersys and MK batteries all came in around 220-230 CCA.

We use the battery tender unit on the batteries for a week or so every month or two.

No matter what the care was, I still wouldn't recommend the Werkers as they both were lower performing straight off the shelf. We even picked the newest ones they had.

Re: Which Battery to Buy?
 

There's an old saying about "assume". Case in point: see his edited post.

Re: Which Battery to Buy?
 

I don't want to assume which saying you are referring to. Can you please clarify?

Re: Which Battery to Buy?
 

Are you sure you don't want an illustration for this? :p

Re: Which Battery to Buy?
 

I love it when people get my subtle dry humor.

Re: Which Battery to Buy?
 

Ether has humor? :ahh:

Sorry for the late edit. I got sidetracked while I was trying to verify the statement I made. It is still in a "I think that's the time recommended to me" category.

Have you performed a controlled test on your batteries? Different matches yield different power usage. Time to data log!

Re: Which Battery to Buy?
 

Jesse,
The indication of a drop of two volts indicates a damaged cell. Check the case and I bet you find a flat spot on one of the corners indicating a drop. Any SLA battery will get hot once it achieves full charge. All current that is not used for reversing the chemical reaction goes into heat. In general, the heat confuses smart chargers. For that reason, all charging should be performed on room temperature batteries.
Our batteries should be able to make it through a summer (3 months) without being charged. Many old timers might recommend they be left on trickle charge but only certain smart chargers will switch on a trickle/maintenance charge periodically. We do not charge over the summer except when participating in post season events. However, once we are back in the shop on a regular basis, we top all of our batteries off. We use a multi-station smart charger that produces a 5 amp charge rate at full charge per station.

Not all chargers are created equal and yours may be intended for 50 amp hour batteries or above. If so, your charger may be producing significantly higher charge currents than the 6 amps stated for these batteries. High charge currents could result in heating and less than optimal charging. CCA testing with a car type test set will result in extremely high and possibly damaging current draws. I recommend the Battery Beak for quick checks and the West Mountain Radio CBA IV for controlled testing.

Re: Which Battery to Buy?
 

Al, not sure if the hot battery comment was directed at my post or not, but our charger/maintainer is a 10 bank 2 amp charger. I'm not denying the fact that a battery will get warm when charging, but the Werker batteries we tried last year got warm immediately and never made it to full charge. This charger isn't going to damage the batteries, nor will the Optima 400 with a setting specifically for mulitple size AGM batteries.

Also, there are many forms of automotive CCA testing meters out there, don't jump to conclusions about what they do. You can't say every automotive tester will damage them (automotive includes motorcycle/moped), however I would accept that certain methods could damage a battery. All of our equipment is recommended and operated with the assistance of an electronics engineer and a lead acid battery specialist that work with us to make sure we can save money on batteries. We still use batteries in competition from four years ago because they still perform just fine and only slightly lower in performance than the brand new ones we get each year.

Re: Which Battery to Buy?
 

Andrew,
If the charger is truly making only 2 amps per output, then batteries should not get immediately warm. Either the batteries are defective or the charger is making way more than 2 amps (as in the charge circuit is shorted). Even with defective batteries, the KOP charger takes a while to heat a battery. The documentation talks about the four charge cycles but it doesn't really explain if the charge current is average or maximum. In general, CCA testers put a very low resistance load across the battery. I would be interested to know the model of the tester you use.

Re: Which Battery to Buy?
 

Thanks for the tips! I will forward this on to a student who can hopefully report back soon.

Re: Which Battery to Buy?
 

This is the reason I can't recommend a Werker brand battery in this application. Ours were hand picked from separate shipments and both showed the same problems. Not a good sign for Werker in FRC. Their large batteries for NECA racing were great however. I will have to check on the tester as it is expensive and they don't let me play with it much. It lives at another mentor's house who owns it.

Edit: This is one of the ones that we use to evaluate our batteries. It is a micro-processor controlled tester that measures the internal resistance of the battery at no load, while measuring the voltage.

Re: Which Battery to Buy?
 

Andrew,
The linked tester looks interesting but the documentation doesn't really document how each test is performed. I have contacted the manufacturer to see if I can get any additional info. My suspicion is that the load test is performed for a very short period of time that is not controlled by the human tester. That makes the test fairly benign. The PBT-50 looks like a more appropriate tester for our size batteries but both should work.

Re: Which Battery to Buy?
 

This stuff is all fairly far outside of my wheelhouse. I know how batteries work and I can take care of them well enough, but my desire to get into the numbers and specifics of testing and data logging is about as strong as my daughter's desire to clean her room.

With that said, our electronics mentor told me that it doesn't technically do a load test. It finds the internal resistance and measures the voltage, then works as a calculator to work through a little ohm's law and gets it's answer. The only downside of the lower models of the Midtronics is that the batteries we use don't generate enough amperage to fully make use of the test. For example, they will most always return a reading of their being a bad or failed cell in the battery simply due to the size of the battery. The PBT-300 allows you to look down to 100 CCA which allows our batteries to be tested to our needs. We will have to test the PBT-50 sometime though and see how it works.

He did mention that the West Mountain Radio tester is something he would be interested in as he has used them before, but $200 is a lot of money for us and we need to make sure we can fund registration before we look at anything like that.

Re: Which Battery to Buy?
 

Andrew,
I received a very informative reply from Midtronics Tech Support on these testers. It is my understanding from the reply that the CCA test does not use a load and does not require a fully charged battery. The test makes a calculation based on a "conductance" test. The test generates an AC waveform that is used to determine the internal conductance of the battery. This is an indication of the available plate area within the battery. That value is then used to generate a CCA display in the unit. This value when used with other tests that the device performs can determine the true health of the battery without a lengthy test. The manufacturer does recommend that any odd readings be performed a second time after the battery is fully charged as well. The full set of readings, if interpreted correctly, can point to a battery with a failing cell or a battery that is nearing end of life and therefore good for practice but not competition worthy.
Tech support also provided me with a document titled "Transportation Battery Testing Q&A" that describes the test in more detail. I also did a search of their website and found this page...
http://www.midtronics.com/transporta...t/technologies
It has several informative articles on batteries and testing. My contact suggested that the larger tester may not give you the most accurate readings on FRC batteries as they are designed with "wet" cell batteries in mind. Since our batteries are not specified in CCA, users will have to come up with a "good" CCA value when using this test.
I would like to thank Midtronics tech support for their helpful and hasty reply. I was fairly impressed with their website and product line. It is easy to see why they are the official battery tester for NASCAR. I would like to see one of these testers in use if anyone has a unit at an event I attend.
Tech support suggested that a MDX-640 might be a better device if a team is looking at Midtronics testers.

Re: Which Battery to Buy?
 

Al,

Thanks for the update, it is a nice little unit and seems to do a great job for us so far. Something seemed wrong to me when I said internal resistance. Conductance sounds better.

The only funny reading we get is the meter tells us we have a failed cell no matter what. Our established CCA value for a competition ready battery is anything over 180 CCA. If they drop below that they are used for practice or for emergencies. A good new battery will typically be in the 230-250 CCA range, with some higher and some lower.

Re: Which Battery to Buy?
 

Andrew,
I can't give you any ideas on your problem at the moment. The failed cell indicator may be coming from the test measurement as it compares to a wet cell auto battery. The tester uses the conductance test to make these determinations. The doc I saw specifically relates the conductance to the available plate area. As a battery ages, sulfation and other things affect how much plate area is exposed to the electrolyte. This is proportional to the available current. The less area, the less available current.

Re: Which Battery to Buy?
 

Tangentially related, I can't wait for the price of LiFePO4 batteries to drop a tad more and then we can skip this lead nonsense completely :cool:

For comparison, the batteries we use are really only 3-6 AH in the FRC context (their apparent capacity is reduced as a function of current draw. This is demonstrated on most manufacturers spec sheets).

The only advantage of lead currently is it's peak current capacity is pretty high compared to it's actual capacity (it's C rating) per dollar.

We'd need to use a LiFePO4 pack larger than 6 AH just to get the peak current we'd need. That's not a huge issue though, it'd let teams run the same battery for multiple matches. Teams like ours would drop from 12 batteries to 3-4, which at current prices makes them cost essentially the same.

We'd also be replacing them less often annually. I think with that they'd actually SAVE money at this point already.

Re: Which Battery to Buy?
 

Learned my lesson with assumptions :rolleyes:

But I agree with this 1000%. Cannot wait to get to lithium, hell even NiMH would be better.....

I may have rigged a LiPo Pack (do not do this...) for my team's FRC bot in the past for in lab testing uses only and man that was heavenly.....

Re: Which Battery to Buy?
 

The price of LiFePO4 (Lithhium Polymer) and LiCoO2 (Lithium Ion) batteries should come down quite a bit in no time, as Tesla's working on creating a large factory in Nevada.

With the massive supply it will create, we should see prices drop quite a bit.

I can't wait till all of this is complete!

Re: Which Battery to Buy?
 

Except for one thing.

Tesla's focus is going to be on making batteries for Tesla vehicles, or I miss my guess. Not a general "let's make lithium batteries" plant.

Now, I'm not going to rule out them getting some of the technology down and releasing it under patent or what-have-you and someone else building a "let's make lithium batteries" plant, but that'll probably be about 5-10 years after it opens at the shortest, 17-20 years more likely.

That said, I know nothing about what Tesla's internal workings are and even less about making a lithium battery. So I could be totally off the mark.

Re: Which Battery to Buy?
 

They actually are partnering with Panasonic heavily, and intend to sell (or Panasonic sells, I forget the exact details) batteries to all markets.

Re: Which Battery to Buy?
 

I agree. Tesla wants to make batteries primarily for it's own vehicles. However, I am sure that they will devote a small portion of their factory to produce consumer-grade batteries with it's own technology.

Re: Which Battery to Buy?
 

Realize Tesla wouldn't exist on car sales alone. A large chunk of its viability is from tax incentives & selling electric car credits to conventional car companies. One hopes it is a seed to bigger & better things. For the battery factory to be successful, at least in the near term they are going to have to make batteries for other than Tesla cars.

We run a LiFe battery on our T Shirt cannon. It great. Lasts for a Football game that normally takes 2-3 FRC batteries. A bit of a pain since it takes a separate charger.

Re: Which Battery to Buy?
 

That is true that it takes a separate charger. My project mentor for Engineering works for SRP and he told me that Lithium batteries are quite safe when used PROPERLY. The only difficulty is charging because as soon as it is full and you continue to dump charge into the battery, it heats up quite rapidly and goes through thermal runaway. This can result in catastrophic events such as rupturing and the spewing of poisonous gasses. However, one nice benefit of Lithium batteries is that they can output a lot of current safely (as long as the wires can handle it). With these SLA batteries, to pull large amounts of currents, we need large batteries, which escalate in price quite quickly. You can get Lithium batteries off HobbyKing, which can provide a much higher current output, and that too for a reasonable price.
Also, one of the nice things of Lithium batteries is that if they are well-maintained, their discharge voltage is quite stable until depleted, where they drop down significantly.

Also, I don't think Lithium batteries require as much maintenance as SLA batteries, which need to be fully cycled every few weeks to maintain it's quality. As long as you bring the voltage down to between 3.7-3.85v per cell, it can be stored with almost no worries.

Also, the self-discharge characteristics of Lithium-based batteries are very good, with a very slow self-discharge rate. Just stow your battery at 3.85v and it should be in perfect conditions after a long summer break, that is if you make sure they are still in the 3.7-3.85v range when you get back.

There are some other emerging battery technologies coming together. My mentor had spoken about Sodium (metal) Chloride batteries, where it uses the energy output from the reaction between sodium (Na+) and chloride (Cl-) to power the systems, and probably some sort of electrolysis to break up the molecules again. These batteries have a magnificent charge capacity, but come with the drawback that they need to be heated to around 300 degrees celcius to melt the sodium.

Please feel free to let me know if I stated any wrong information. A lot of this is from when I was doing battery research for the MicroCar that I want to design.

Re: Which Battery to Buy?
 

Yash,
Those first two things are some of the reasons we don't want them on FRC robots. Our batteries get dropped a lot during competition.

I am not sure what you mean by SLA battery maintenance. These are sealed batteries and there is nothing you can do for maintenance except to charge. While they likely will not tolerate no use for a year or more, a few months is not a problem.
I recommend you check out the Battery University site for some really good info on batteries.

Re: Which Battery to Buy?
 

We've had pretty good luck with our Enersys batteries, as have others, so I'm curious why you exclude them from the running? We bought a bunch in 2011, and have been acquiring more with the KOP since, and they all worked well this season, even with our admittedly lousy maintenance.

Re: Which Battery to Buy?
 

I know the Enersys work great; I've driver coached with them for many years. They too sometimes get bad cells, but I was curious about experiences with other batteries.

In all of our deconstruction of last year's "stuff", I totally forgot to check on the batteries last night. I'll have to report on this some time next week.

Re: Which Battery to Buy?
 

Interesting....I kind of like sticking with what works.

On the topic of LFP batteries, I was poking around the internets....

http://www.powerstream.com/LLLF-12v.htm

Re: Which Battery to Buy?
 

It is not that difficult for these batteries to be used "Properly". Typically, they have much higher ratings than lead acid batteries, yielding a much harder to reach "danger zone". Some Lithium Polymer (LiCoO2 gelled) batteries can handle currents as high as 250 amps/hour. Most of these batteries are only dangerous when subjected to mechanical parts that can poke or puncture the packets.
Lithium Polymer/Ion batteries can be used quite safely if just a couple guidelines are met. Some of the ones I can think of at the top of my head include:
-Use a hard case (so the cells are isolated from sharp parts)
-Use good safety measures. A properly-rated fuse, built into the battery (for ICOE), an external fuse for excessively high currents that don't reach the battery's limit and then, all the current FRC safety measures should suffice!
-USE THE RIGHT CHARGER

I really think that the cons of Lithium-based batteries are quite sparse as compared to the pros.
I really believe that FRC is not making the move to renovate the battery technology because GelCel Lead Sulfuric Acid batteries have proven their existence to be reliable. After all, they are the oldest technology for rechargeable batteries. This is the reason why we cannot blame the experts for their decision. However, as long as the safety specifications are met, the newer technologies are extremely safe.
It is EXTREMELY uncommon to have our telephones explode when we drop it or keep it plugged in overnight. Arguably, one could say that the batteries are smaller. Yet, they contain similar (or even the same) chemistry and reactions and are equally as succeptible to these failures. I guess that a cell phone battery explosion is not as spectacular :D as a Lithium car battery substiture, but they are equally as dangerous.

In short, Lithium-based battery technologies are not as dangerous as feared to be. An integrated charge controller can be used to maintain charging safety. A thermal resistor can be used to shut down the battery in case of an approaching thermal runaway. A fuse/breaker can be used to ensure that the battery maximum ratings are never reached.

Not to mention, How light are Lithium batteries. I would not have to be as scared to drop a lithium battery (as long as the casing is strong) on my foot as a lead sulfuric acid battery.

Mr. Skierkiewicz,
you were speaking about lead acid maintenance. Gel-cel batteries are not meant to be maintained. They are not supposed to require hydration. The main caveat to this sealed design is sulfation. You cannot do much to prevent this process from happening, especially at the juice we pull out of these cells. Thankfully, newer Lithium-based designs do not experience as many lost chemicals due to a similar process!

Re: Which Battery to Buy?
 

LiFePO4 chemistry doesn't have the safety issues of other Lithium chemistries.

I'd argue they're actually safer than the SLA for FRC use.

Re: Which Battery to Buy?
 

Precisely said. With the loss of some energy density it provides much safer operation. There are some emerging technologies such as lithium sulfur and lithium air, which are inert, even in air. These types of batteries are surely much safer than lead acid batteries. Lead

Also, prices are coming down significantly as more manufacturers of these batteries are quickly emerging, so soon, lithium batteries might be more practical (if not already) than SLA and it's close alternatives.

Re: Which Battery to Buy?
 

I was thinking the same after reading more about LiFePO4 a few days ago.

Re: Which Battery to Buy?
 

I think SLA will be around for quite some time at FRC due to its track record. I've been to one event in my entire FIRST existence where a venue was evacuated due to a battery spill (2014 Greater Pittsburgh Regional). I don't know much about the variations in LiFePO4 manufacturing, but I imagine this would weigh highly on it being allowed in the future.

Nuclear fission is safe. Can I use that? :]

LiFePO4 see some extensive use at the University Rover Challenge. Check it out if you want to be part of a growing, challenging competition at a university level!

Re: Which Battery to Buy?
 

It's easy to say that you shouldn't abuse batteries but I've seen people accidentily drill into their battery and the type we use now is surprisingly forgiving.

Re: Which Battery to Buy?
 

There is no way to prevent mistakes like this from causing a dangerous environment. However, Why is the battery in place while someone is working on the robot?

However, there are new chemistries on their way out, like Lithium Sulfur, which have solid electrolytes and are much less likely to explode in case of a puncture!

Most of the sources where I gathered this info isn't what I would call reliable. I got most of my information off Chinese battery manufacturer websites :o .

However, I did come across this article, which seems to be a good source.

Re: Which Battery to Buy?
 

Take a LiFePO4 battery and drill a hole in it, and then attack it with a propane torch. It'll turn out pretty safe given the action. You can also discharge to 0V and bring the battery back to life.

The only disadvantage of a LiFePO4 battery is it's current capacity per cost. If you need 600 AMPs, you can get that cheaper with SLA. However, it's pretty much at the breakeven point when you consider that we can use less batteries, and that the batteries don't need to be replaced as often.

LiFePO4 also doesn't need balancing, and technically could be charged with an SLA charger (it is suboptimal). Reasonable priced non-balancing LiFePO4 chargers exist too.

Re: Which Battery to Buy?
 

Correct me if I'm wrong here, but if I recall correctly, LiFePO4 batteries tend to have their own internal balancing circuits (or maybe it's just the brand I'm familiar with that has 'em).

I'd actually go so far as to say that some types of LiFePO4 batteries would be just about a drop-in replacement for SLAs in FRC robots, if their cost came down a bit. I've worked on a non-FRC robot that, for redundancy purposes, ran two LiFePO4 12V batteries, just about the same size as the current SLAs, on two separate circuits, driving RS-775s and linear actuators. Never had an issue with the batteries. Not sure if they got charged much during competition at all.

Re: Which Battery to Buy?
 

They can, but that will inherently reduce ability to source current (or add a lot of price).

They can be run w/o any balancing circuitry in the cell or the charger w/o issue. It just reduces the total # of cycles it can do. This is still more than enough cycles for an FRC team.

Re: Which Battery to Buy?
 

Here's a way to make it safe to drill into a battery: choose a battery type that doesn't have a violent reaction when a cell is breached. For example, the type we use currently or, according the AdamHeard, LiFePO4.

Also, your team might remove the battery before working on the robot but it seems to me that most teams don't. Maybe I haven't been looking closely enough, but it's seemed to me that at competition the only time a team removes a battery is to put a fresh one in.

Re: Which Battery to Buy?
 

That might very well be true, especially at competitions. Next thing we know is we are putting tungsten (or stronger) casing around the battery :D.

I really don't think there is any protection against stupidity other than brain!

Re: Which Battery to Buy?
 

Stupidity and poor guidance/supervision are very different things (although their consequences can be equally devastating).

Re: Which Battery to Buy?
 

OK,
I think we need a battery expert to step up here but in the absence of that knowledge, I spent a couple of hours researching this over the weekend. Some of the things that are needed here are a battery that will not self destruct when mishandled or when max discharge currents are exceeded. I went looking for batteries with the same characteristics as our current battery. So starting a search with 12 volt and 18 AH and Lithium I came upon a wide variety of battery types and specifications that actually fit in the same size as our current battery. What I found is this. Very few of the batteries listed as "starter" batteries give any specification sheets. On one site I was actually denied access to the linked file. What I was not able to find was exact specifications as to internal resistance or to AC conductance for any Li battery in this class. What I backed into was internal resistance of typically 6-14 mohm per cell for most of the Li types. While the cell voltage is higher in Li (and therefore less cells are needed), that still amounts to more than twice the 11 mohm total for our batteries. A peek at peak current also limits Li batteries in this class to less than 200 amps, about a third of what our SLA batteries are rated. In some batteries there is actually a internal electronic breaker to shutdown the battery when the current exceeds ratings, to prevent catastrophic damage. Most manufacturers warn that exceeding max current leads to thermal runaway. That is where the temperature of the battery skyrockets in an uncontrolled fashion and sets itself on fire. Yes, the Li batteries in this class have better labels, stating they are 20 AH or higher.
Yes they can easily deliver currents at 3C and maintain cell voltage almost until they are depleted, but we do not ask batteries to do that. Yes, they are half the weight, but we don't weigh the batteries. Yes they can deliver impressive currents, but please remember that CIM motors stall at 131 amps. While most teams cannot effectively design a robot to meet the needed series wire resistance to deliver that, it is not uncommon for them to produce more than 100 amps per motor. How many of you use 4 CIM drives or even more? As to the linked Li-sulphur, please note that in the article it states that the sulphur will breakdown within a few cycles rendering the battery useless.
So when looking at all of the factors, weight, max current, reliability, cost, and ability to withstand most abuse, the AGM SLA we use seems to be the best of all worlds.

Re: Which Battery to Buy?
 

I design battery systems. That knowledge is in the thread already ;)

Most of the above you looked at is likely NOT LiFePO4. LiFePO4 handles more total cycles, and isn't nearly as damaged by deep discharge as SLA is. These will lead to some big savings and higher reliability for teams.

A LiFePO4 pack could be made for $200 that would be the functional replacement of 2-4 SLA batteries, and be able to source the current required.

Re: Which Battery to Buy?
 

Adam,
Could you link some spec sheets? I am interested in the series resistance specifications and peak currents and basically anything else you can pass along.

Re: Which Battery to Buy?
 

I would want to use pouch based cells for price/space reasons, but a lot of those aren't public facing in terms of spec. You need to talk directly to manufacturer.

In terms of raw chemistry, these are the same as many top LiFePO4 and will perform very similar.
http://www.k2battery.com/products-26650P.html.

It's not uncommon to see 50C ratings as the burst discharge.

It's also not uncommon to see burst at 10C or so for the same chemistry (or have a protection circuit that artifically limits the burst rating, which isn't necessary for FRC). Obviously these cells/packs wouldn't be what we use.

EDIT: Here is spec for pouch A123 cell. http://www.raceyard.de/tl_files/News...Data-Sheet.pdf
This one is interesting in that it also specs all the safety tests it passed.

Re: Which Battery to Buy?
 

A123 batteries is actually where I started my battery research. However, I was not able to find enough information to validate what they had in their datasheets and what they sold.

Re: Which Battery to Buy?
 

Here's a battery I was looking at the other day:

http://shoraipower.com/lfx18l1-bs12-p94

Smaller in size, less than 2.5 lbs, 270 CCA, but say they are conservative and this is closer to 405 CCA in lead acid ratings according to thier FAQ. Never heard of the company before, but thier batteries have good user reviews on amazon. I asked for more info, I'll let you know if I hear anything back.

Re: Which Battery to Buy?
 

I wouldn't recommend them. I bought one to check it out.

Only after purchasing did I realize when they say Pb Eq AH, they mean 3x actual capacity. Discharge test showed that they actually only hit about 25% of advertised capacity (versus 33%).

So, their 18 Ah batteries are actually 6. This is done to account for the approximate 3X+ derating lead batteries get at high current discharge.

They are packaged nice, but a bit spendy.

Re: Which Battery to Buy?
 

Their website is another exercise in frustration. Few Li manufacturers actually publish helpful info. CCA is not a good indicator for us. We need hard facts like internal resistance, discharge curves and other hard data.

Re: Which Battery to Buy?
 

Here is Shora's logic for how they rate their battery compared to a SLA. Their market seems to be drop in replacement for motor vehicle batteries. Motor vehicles (older ones especially) have very simplistic charging strategies.
From Shora FAQ

Re: Which Battery to Buy?
 

Ya gotta love marketing people.

Re: Which Battery to Buy?
 

I agree with Al quite the marketing spin. Lead acid battery mfgs use CCA to indicate the cranking ability of their starter batteries and reserve capacity to indicate how long they can deliver power at a moderate amperage. You won't find an Ah rating on an automotive starter battery.

Re: Which Battery to Buy?
 

Drifting off the batteries for FRC subject... Considering the Shora battery is 2-3 times the cost of an equivalent Lead Acid battery it replaces. The low self discharge is appealing for vehicles that sit for extended periods. Like collector cars, motorcycles, boats, ect. But to get a consistent full charge on the battery you still need an external charger. So you might as well use a battery tender with a lead acid battery.

The advantages Shora claims, while written in marketise is consistent with what the mfr. of our tee shirt cannon Li-Fe battery told us & bears out with use. The Li-FE battery is a lot smaller & lighter than the deep cycle lead acid battery I would have used in its place.

Re: Which Battery to Buy?
 

Shorai batteries aren't who we should be looking at.

If we get an equivalent LiFePO4 battery it will be true 15-20 Ah (versus the 4-6 the SLA ones ACTUALLY are), and will last for many matches. It will also not get wrecked from deep discharge, or from sitting discharged for a while. This combined with a much higher number of total cycles it can do means they would quickly pay themselves off.

We go through 10+ batteries a year due to how much we practice. That number would be greatly reduced.

Re: Which Battery to Buy?
 

Cell manufacturers will provide all this if prompted.

Re: Which Battery to Buy?
 

Which company do you work for and what are the applications for these systems?

Side note, I consider the SLABs we use to be 10Ah, as that is spec capacity at the 1 hour rate. We've tested them at a 10A discharge and they produce 14Ah new. Also, If you're going through 10 batteries a year, I'd like to see what you're doing during practice. I do believe you are doing something which is shortening the life of the batteries.

Back on thread... I work with Aircraft Batteries as part of my job, including Lithium Batteries (not Boeing 787). I still see lithium batteries as too dangerous for use in FIRST. This includes LiFePO4 batteries. The failure modes of lithium batteries are still too dangerous and can produce toxic gases fairly easily. When combined with the abuse from personnel who will not know how to handle them properly and the robotic impact environment, we're going to burn down a building if we use them.

Re: Which Battery to Buy?
 

Trust Automation, can't comment on what the applications are.

We practice a LOT, and do it year round. That easily goes through 10 per year. We're not the only team that does this.

Re: Which Battery to Buy?
 

We purchase at least 10 new batteries every year.

Re: Which Battery to Buy?
 

That is $450 spent right there! Instead, it would be better to invest in a more expensive battery ($100 per battery instead $43.50 (AM)) that lasts several years!

I highly doubt that there are going to be batteries like that. However, what is a deal is struck between USFIRST and a battery manufacturer such as A123 Systems?! I think that the price per battery would drop significantly for FRC teams all of a sudden!

Re: Which Battery to Buy?
 

That sounds like a real problem....for maybe 2% to 5% of teams?

The rest of us get by using the same batteries for several years.

Re: Which Battery to Buy?
 

Everyone who uses the same batteries for several years would likely have better performing robots if they weren't forced to do that.

Re: Which Battery to Buy?
 

I'm sorry, I didn't really get you so my reply might be off topic. Typically, batteries will have a decline in performance as they age. This is due to chemical processes such as sulfation. I guess that the team would slowly accommodate to the aging of these batteries by making their robots more efficient, but there's a dead limit before it becomes impractical. It would be nice to have a robot that isn't a dead piece of equipment due to 10 year old batteries :D (I wonder if that would even be legal :D).

Also, as batteries grow older, their "C", or Charge rating declines. This means that these batteries can pump less juice safely and effectively.

Re: Which Battery to Buy?
 

Yash, what he's saying is that because of the reasons you mention, teams that are "forced" (due to finances or other reasons) to compete with the same batteries for several years aren't going to perform quite as well as teams that buy new batteries every year (and mark the older ones as "practice" if they even bother to keep them).

Re: Which Battery to Buy?
 

There is one variable that has not been touched on in this thread. The original post talked about problem post season. How much did the impacts the robots endured this year affect our battery life?:confused:

Re: Which Battery to Buy?
 

Most of us have other things hampering our robots' performance more than battery degradation...

Re: Which Battery to Buy?
 

Following this logic, nothing should be improved ever because many teams have trouble with ________.

Re: Which Battery to Buy?
 

Or, we have other priorities. Mostly, getting a robot built.

I'm surprised y'all haven't come up with some lithium batteries for use during practice. I'm sure we'd all like to hear about some experiments in this area.

Re: Which Battery to Buy?
 

I've used RC grade LiFePO4 packs to run a practice bot w/ no issue. 13.2V nominal, 16.8 Ah. It passed the subjective test of a few minutes of practice.

Others have done experiments as well.

Re: Which Battery to Buy?
 

At some point the FRC market will be large enough for a custom designed battery. Are we there yet, maybe not. It is interesting to think about though.

3500 frc teams x 4 new batteries a year per team average x 43.50 per battery = $609k spent on batteries per year for frc?

If we assume for every battery a team buys, it has to take one out of service, thats about 14,000 lead acid batteries to properly dispose of a year?

(I admit my numbers are likely off, just food for thought)

Re: Which Battery to Buy?
 

Unfortunately, that's not a lot of money at the end of the day.

I don't see what benefit (from a business case) a custom battery would provide. It's definitely an interesting thought though.

In my experience, we (836) took only a few batteries out of service since we started paying attention to how we use the batteries 4 years ago. I doubt we [ab]used them as much as 254 does, but they will last more than a season or three if properly maintained.

Re: Which Battery to Buy?
 

Adam, can you comment on relative profit margins of battery production, when selling wholesale? If not, that's cool too.

Re: Which Battery to Buy?
 

The problem with a custom battery is you would have to provide it world wide. Including places with difficult customs laws. I think custom in a FRC sense would be standard cells in a custom case. Much different & simpler than designing from scratch.

A possible first step would be running them in a off season competition where the rules are little more relaxed?

Re: Which Battery to Buy?
 

Guys,
We do semi yearly checks with a CBA III analyzer and some of our batteries are still performing well from 2012. Some (one) from 2014 failed. Not all batteries get the same usage all year long as hard as we try to rotate.
Last year we were at 2700 teams +/- with about 400 rookies. But we all know of some really good teams that simply will die each year. It is part of real life for us. Some great people will step away, retire, change jobs or school districts will decide to spend money in other places. It happens.
Under our use, I estimate we should get around 400 charge/discharge cycles. Some teams more than that. As Frank mentioned, we are international and what is common and not so expensive here can be 50% higher just across the border in Canada or Mexico and may be considered hazardous in Israel or Europe. We also have to consider traveling and air transport of these devices.

Re: Which Battery to Buy?
 

That is what I have been attempting to suggest. Don't reinvent the wheel. Just make it better!

Re: Which Battery to Buy?
 

We also seem to get about 2 seasons (some more, some less) before we see the batteries start to fall off also, it's important to check. We load test with something similar to this:

http://www.amazon.com/gp/aw/d/B000AMBOI0?cache=cf334507e5e6604863e134ace7b1c657& pi=SY200_QL40&qid=1412860949&sr=8-1#ref=mp_s_a_1_1

We compare the voltage drop under load of the batteries and classify them as competiton or practice. This has worked well for us for a number of years. We can check them in a few seconds at competition also.

Re: Which Battery to Buy?
 

I purchased that exact model a while ago to run some tests. In my tests it did not detect weak cells:

http://www.chiefdelphi.com/forums/sh...44&postcount=4

Re: Which Battery to Buy?
 

I have seen that discussion before. Agree capacity testing a couple times a year would be even better.

How many batteries you try before finding one that can pass high load test, but fail capacity? Is capacity fail first more common than high load fail?

Re: Which Battery to Buy?
 

For practice, we've run deep cycle marine batteries that are used in our school electric car team. They work very well, but they have a different internal resistance than our FRC batteries, so the robot behaves differently. This is noticeable in autonomous mode.

Re: Which Battery to Buy?
 

Since we know the types of batteries this year, are there any that you would/ would not recommend?

Re: Which Battery to Buy?
 

As testing batteries came up... Attached is some sample code and a quick writeup on how to perform a full battery capacity check using equipment from the 2015 KOP and under $40 in resistors. I had two of our students code this up quickly so we could see which of our batteries need replacement.

Re: Which Battery to Buy?
 

Here's a home-brew battery tester if you can't spare $40 or you don't want to use your KoP PDP:

http://www.chiefdelphi.com/forums/sh...8&postcount=12

http://www.chiefdelphi.com/forums/sh...8&postcount=33

Re: Which Battery to Buy?
 

Don't trust the Battery Beak too much. We (Bomb Squad) have a CBA (Computerized Battery Analyzer) which drains the batteries to dead, 10.5 volts, and measures the amp hours. This is very accurate as it measures the whole life of the battery whereas the beak only applies a very small load for a very short amount of time. This makes it very inaccurate and right now we are working to find a correlation between the CBA and the Beak and post it for use. I hoped this helped in some way.

Re: Which Battery to Buy?
 

I wouldn't call the Battery Beak "very inaccurate". Of course the CBA is a better test, but the Battery Beak is accurate enough for its purpose, which is to quickly determine the state of batteries at competition. The CBA's test takes upwards of a few hours, the Battery Beak's test takes only a few seconds.

Re: Which Battery to Buy?
 

Our team has used the Genesis for our robot since 2013 and haven't had any problems with it holding a charge

Re: Which Battery to Buy?
 

Sean,
The only way to correlate the two is to set the CBA to the same load. The Beak uses two resistors one a very light load and one a heavier load and then makes a calculation based on tested impedance and displays the result of the calculation.

Re: Which Battery to Buy?
 

Correlation comes in many flavors. What sort of correlation did you have in mind?

Perhaps a statistical correlation between internal resistance (as measured by Battery Beak) vs amp hours (as measured by CBA at various loads) ?

Re: Which Battery to Buy?
 

I'd like to know if you can detect bad cells with this correlation as well. We've seen individual cells drop out after 30 minutes and the battery continued to discharge for another 30 afterwards (I think I still have the plots for this one)

Re: Which Battery to Buy?
 

For batteries with bad cells, the jury is still out. There is some anecdotal evidence that bad cells will not necessarily be detected by the BB internal resistance test.

That's why some teams test their batteries at the beginning of each season with CBA (to weed out the bad ones), and use BB at competitions to check the bot's battery before rolling the bot out to the field.

Re: Which Battery to Buy?
 

Based on experience from you and others here, the theory seems to be:

1. Any battery that fails the battery beak or a high current load of 100+ amps should correlate to reduced capacity.
2. Vice versa, a battery failing capacity may or may not correlate to a fail based on a battery beak or a high amp test.

Some examples that demonstrate these situations would be helpful to the community.

Re: Which Battery to Buy?
 

I was wondering what CBA bomb squad purchased? It would be great if you could find a link.

Re: Which Battery to Buy?
 

Lately we've had our older Genesis batteries from 2012 expanding and become very hot. We will never get these again.
The MK's that we've used previously and this year is what we will stick to from here on out.

Re: Which Battery to Buy?
 

Under what conditions was this occurring? During use? During charging?

Re: Which Battery to Buy?
 

This was during charging.
We would come the next day and the whole place would stink up.

With the MK's that we used in the past, we could have them on the charger continuously for years and never had issues with them.
They obviously didnt hold their charge as before, but other than that, no issues.
I should have taken a picture before we disposed of a few more this past weekend.

Re: Which Battery to Buy?
 

Have these batteries been abused at some point? This is very unusual since Enersys is one of the premium battery brands. You may want to check your charging current.

At work, we have used tons (literally) of the 7AH version of the Genesis battery, every week, for at least the last 10-12 years without seeing this symptom. They are used in UPS and are on trickle charge continuously until there is a power outage. The UPS' they go into are used to run hospitals (yes, the whole building), data centers, air traffic control systems and other critical infrastructure. There is even one at the observatory on Maui. We do recommend that our customers replace the batteries every 3 years since they start losing capacity. Our Field Service people do run into symptoms like this when customers replace the batteries with cheaper brands.

Re: Which Battery to Buy?
 

Our batteries havent been abused at all. Since we started doing FRC, we have charged them in the same way and fashion. We never experienced any battery issues (other than losing capacity) until this year with our 2012 Enersys stock throughtout the past several months. Earlier this week, we just decided to dispose of them all to prevent more of them having similar symptoms. We normally used the MK ones over the years, but in 2012 went with Enersys instead.
Strange.:confused: