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Unread 19-08-2014, 16:14
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Batteries

Our team has been using the standard Enersys NP18-12 batteries for the last several seasons. We typically buy a new set of competition batteries every year or 2 and relegate the old batteries for testing and practice. With the expansion of the list of legal batteries this past year we are looking for feedback from teams that have experience with batteries other than the Enersys NP18-12. We had a battery start leaking this weekend around the top seal and are looking to replace batteries this coming season and would like to know which batteries are “top quality” and which have a reputation for not holding up. Our experience with the Enersys batteries has been hit or miss. Some seem much better than others. For reference we have a nice battery testing setup including a West Mountain Radio CBA with dual 500W amplifiers. We are building new battery charging station(s) this fall around Autometer BusPro-660 chargers and are looking to replace our competition batteries with “top quality” batteries. Now that we have a competition season behind us does anyone have any advice on the “best” batteries to go with based on the 2014 legal battery list*?:

Enersys (P/N: NP18-12)
MK Battery (P/N: ES17-12)
Battery Mart (P/N: SLA-12V18)
Sigma (P/N: SP12-18)
Universal Battery (P/N: UB12180)
Power Patrol (P/N: SLA1116)
Werker Battery (P/N: WKA12-18NB)
Power Sonic (P/N: PS-12180 NB)
Yuasa (P/N: NP18-12B)
Panasonic (P/N: LC-RD-1217)
Interstate Batteries (P/N: BSL1116)
Enersys (P/N: NP18-12BFR)
Enersys (P/N: NP18-12B)

*Yes, we know what was legal last season may not be legal next season.
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Unread 19-08-2014, 16:47
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Re: Batteries

Hey Chuck, I have been very happy with the MK batteries. If you call them and tell them you are a FIRST team they give you a pretty good deal. We have paid about $40 each including shipping. We normally order 6 during each build season.

They're customer service has been great. We had an event we needed the batteries for and they were able to work it out with the UPS driver to deliver the batteries to me in a parking lot after they got picked up from their distribution center in Houston. It was pretty crazy.
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Unread 19-08-2014, 17:03
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Re: Batteries

Quote:
Originally Posted by AllenGregoryIV
They're customer service has been great. We had an event we needed the batteries for and they were able to work it out with the UPS driver to deliver the batteries to me in a parking lot after they got picked up from their distribution center in Houston. It was pretty crazy.
Did you use the batteries that weekend? Did you cycle the new batteries a few times before using them in competition or did you use them fresh?

-Nick
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Unread 19-08-2014, 17:07
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Re: Batteries

I know it doesn't exactly answer your question, but check out your local Batteries Plus. They usually don't have a lot of variety, but they'll likely have something that's on the approved list. Also, if you register with them as a corporate account (all it requires is a phone number, and they've never called me) you get a rather large discount... I want to say it was almost 3 for the price of two last time I went! At any rate, that should save a little bit on shipping!
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Unread 19-08-2014, 17:12
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Re: Batteries

I used YUASA or Power Source at work for emergency lights, emergency notification systems and fire systems. They would perform better than some other brands we used. I never seemed to have any issues. Even under extreme loads, they did not have to be replaced as often as I thought.
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Unread 19-08-2014, 17:29
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Re: Batteries

Thanks for the info so far guys. For clarification by "best" batteries I'm not necessarily looking for cheapest. As with anything, I know some batteries are better quality than others but I don't really have enough experience with different battery brands to know which are "high quality" and which to avoid. My philosophy is EVERYTHING on the robot starts with the battery so why risk using anything less than the best quality. We all pay a lot of money per match to play in FRC and I have seen may teams loose many matches because of battery issues over the years. Why risk it with el cheapo batteries? I just don't know which on the list have the best reputation for quality.

We have always gotten our Enersys batteries from Portable Power Systems: http://www.portablepower.com/12_volt...nesis_NP18-12B

I'm not saying at all that we are unhappy with the Enersys batteries and in the absence of info as to a better option I would likely buy more Enersys from PPS tomorrow if I had to. I'm just wanting more info from the collective FIRST community to make a more informed purchasing decision between now and whenever the time comes. I figure everyone would like the benefit of knowing what batteries seem good and what seem not so great. With a few thousand teams using probably tens of thousands of different batteries now there has to be some good and bad recommendations especially given how opinionated folks on CD can get.

So, I have one vote for MK from Allen so far...
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Unread 19-08-2014, 18:43
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Re: Batteries

Quote:
Originally Posted by pwnageNick View Post
Did you use the batteries that weekend? Did you cycle the new batteries a few times before using them in competition or did you use them fresh?

-Nick
We used them right away and I don't remember having any problems.

We have been testing batteries using a CBA III this summer and plan to continue during the year.

If anyone is interested here are the first test results, these aren't that useful until we start seeing what happens to them over time. We also didn't run baseline tests on them when they were new either.

https://docs.google.com/spreadsheets...g0_mqTdVg/edit

These are tested at a 7 AMP drain and a cut off voltage of 10.5 Volts.

Here is a sample graph from one of the the battery test.
https://docs.google.com/file/d/0B0dr...VYNF94THc/edit
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Unread 20-08-2014, 07:36
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Re: Batteries

For those of you that are using the CBA, I recommend that you test at 7-10 amps and 8 volt cutoff. This will give you curves that match the manufacturer curves for most batteries. The CBA has a top current draw of about 7.5 amps, the CBAIV will do a little more. It helps to test batteries once or twice a year and use the overlay feature to see the difference in tests.
BTW, let West Mountain know you are a FIRST team, I have been trying to get them to be sponsors for a couple of years. They are located in a Milwaukee suburb.
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Unread 26-08-2014, 16:32
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Re: Batteries

Quote:
Originally Posted by AllenGregoryIV View Post
6 during each build season.
Why so many every year? As long as you take care of them during the off-season, they should be fine for many seasons of use. My team still keeps around a couple of 2011 batteries because they actually perform just as well as the batteries we got this year.

Quote:
Originally Posted by nighterfighter View Post
But its definitely possible to have the robot operate at dangerously low voltages, so it might be relevant to test the battery down to low voltages.
To my knowledge, the lowest our DS has ever read in-match was 5V during a brutal pushing match. It is very important to know how your batteries perform at low levels.

Quote:
Originally Posted by ChuckDickerson View Post
Do you typically run a fresh fully charged battery at the beginning of each match or is it possible the batteries had been used in one or more matches previously?
Our team rule is one match per battery per day. We put a freshly topped off battery in the bot at the start of every match and don't use it again that day if we can avoid it.
We do our best to avoid using the same battery more than once a day. Our battery box holds 12 batteries and uses a raspberry pi to automatically cycle through the batteries and charge 3 at a time, so we never have a problem with having enough charged batteries. Of course, there are times that a battery must be used more than once per day, and as long as it has had plenty of time to sit, it should be okay.
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Unread 26-08-2014, 17:05
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Re: Batteries

Quote:
Originally Posted by evanperryg View Post
Why so many every year? As long as you take care of them during the off-season, they should be fine for many seasons of use. My team still keeps around a couple of 2011 batteries because they actually perform just as well as the batteries we got this year.
We like to run new batteries. One of the reason we are testing them more now is to see if we can judge the differences better and maintain them better. We also give away some of the batteries that we no longer think we need to young teams. $250 in batteries isn't that much for what could be the most important part of the robot, with out the battery nothing else works.
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Unread 26-08-2014, 22:29
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Re: Batteries

Quote:
Originally Posted by AllenGregoryIV View Post
with out the battery nothing else works.
[tangent alert] You could say that about much of the robot though.
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Unread 27-08-2014, 01:44
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Re: Batteries

Quote:
Originally Posted by BBray_T1296 View Post
[tangent alert] You could say that about much of the robot though.
I'll admit I could have worded that better. What I meant is that it's the beginning of the power path so it affects the performance of all other systems.
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Unread 27-08-2014, 08:53
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Re: Batteries

Allen,
The mechanics of this bad cell failure (in my best guess) is that through damage, either drop or robot hit, some of the plates in a cell become dislodged from the connecting terminals. As such the remaining plates still function normally but the cell has a lower amp hour rating as it will become depleted before the other cells. If we were to test at full current, it might show as a change in available current at 400-500 amps. When testing at the manufacturer's spec, you will see the battery run a normal discharge curve, in some cases more than hour, before the bad cells actually become evident. To visualize, say a cell has 10 positive plates and 10 negative plates. The battery gets dropped and one of those plates either cracks or comes completely off the output terminal plate. Since the plate area is directly proportional to the available current and the amp hour rating, any reduction will reduce both of these measurements. The CBA testing will establish a fixed current load that will calculate the amp hour rating without the need to measure max available current. Since both are affected by damaged plates, just knowing that a reduced cell amp hour rating is enough to declare the battery "practice only". Close examination of the battery case will almost always point to case damage from the drop or hit. If you search "AGM internal structure", you will find a variety of pictures and other links to get an idea of what could go wrong internal to these batteries when dropped.
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Unread 27-08-2014, 11:48
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Re: Batteries

Quote:
Originally Posted by Al Skierkiewicz View Post
Allen,
The mechanics of this bad cell failure (in my best guess) is that through damage, either drop or robot hit, some of the plates in a cell become dislodged from the connecting terminals. As such the remaining plates still function normally but the cell has a lower amp hour rating as it will become depleted before the other cells. If we were to test at full current, it might show as a change in available current at 400-500 amps. When testing at the manufacturer's spec, you will see the battery run a normal discharge curve, in some cases more than hour, before the bad cells actually become evident. To visualize, say a cell has 10 positive plates and 10 negative plates. The battery gets dropped and one of those plates either cracks or comes completely off the output terminal plate. Since the plate area is directly proportional to the available current and the amp hour rating, any reduction will reduce both of these measurements. The CBA testing will establish a fixed current load that will calculate the amp hour rating without the need to measure max available current. Since both are affected by damaged plates, just knowing that a reduced cell amp hour rating is enough to declare the battery "practice only". Close examination of the battery case will almost always point to case damage from the drop or hit. If you search "AGM internal structure", you will find a variety of pictures and other links to get an idea of what could go wrong internal to these batteries when dropped.
I understand that Al. My question is have you seen a case were this only showed on a test with a lower cut off voltage than 10.5V. We don't test lower than that, so I am wondering if we should every once in a while. Perhaps, if a battery has been dropped we should test it down to 8V just to be sure.

Part of the reason we don't test that low is to save time and part of it is because, though observation only, batteries that are drawn that low (always on the robot or powering an inverter) don't seem as healthy afterwords but that could just be observation bias.
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Unread 27-08-2014, 13:45
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Re: Batteries

Yes,
The cell may be just shy of running out of energy at 10.5 volts. For that matter even the lower cutoff voltage may not show a partially damaged cell. The lower voltage will catch more defective cells than at 10.5 volts in my opinion. In some cases, internal temperature may exacerbate the intermittent connection. I had one battery that confused me for a while because when the cell got close to dropping off the graph, it suddenly produced a lot of "noise" over a period of 20-30 minutes before dying. These voltage peaks and dips were several volts. I came to the conclusion that the cell had partial damage and the noise was caused by the plate intermittently making and then breaking contact with the terminal plate.
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