Can you use the same battery for a long time and just recharge it when needed? Also, how can I estimate or calculate how long batteries last? How can I optimize the battery usage? Thanks in advance!
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Against my better judgement we have used batteries over and over again season to season. This is not recommended ( I would say you should be moving batteries to practice bots and purchasing new for competition ), weâve finally be able to after 7 years buy new ones for this season. Try to maintain 6-8 batteries in circulation for events. Many teams may not be able to do this due to available batteries they have.
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Batteries tend to last 1-2 seasons at peak condition. You can test if your battery is still good by doing an empirical test where you basically drive crazy for 5 minutes and if you donât brownout then youâre fine or do a more proper test with the CBA and check if you are above 12 amp hours. Using the same battery for code purposes for a long time can impact how accurate your code is, especially if you are doing autonomous programming with no feedback
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Another note on batteries. The connections of the wires to the terminals can be just as important in battery performance. Iâve tested a battery with a battery beak which gives charge percentage and status among a couple other details and had it show up as bad. I tightened up the bolts on the terminals and the status showed up as good. It is still important to replace your batteries over time, but itâs worth checking the connectors before you declare a battery bad.
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Ar you asking about the long term durability of the batteries or how long you can run your robot before you have to recharge your battery?
Kind of both xD
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Just like any rechargeable battery, it will have a limited number of uses before itâs no longer good. Top tier teams are probably buying a whole new set of competition batteries every season and sending the rest to practice. A team with lower resources or simpler robots can definitely afford to push this another year or two. Over time the performance of your battery will go down.
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Batteries naturally degrade over time.
They degrade faster with other conditions too, like lots of charge cycles, heat, over discharge, over charge, and with different current profiles
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There is no nice way to calculate how long a battery will run your robot due to the large number of variables involved. In general, one should not run the battery below around 11.0 to 11.5V since continuing to run it will lead to permanent damage of the battery.
Some brands/models of batteries will have greater energy storage capacity and will run your robot longer. Others have lower capacity. The weight and complexity of your robot will also affect the run time. A particular battery will run for longer before needing to be recharged when used on a lighter, less complex robot since it uses less energy. Conversely, the same battery will need to be recharged sooner if used in a heavier, more complex robot that uses more energy.
I would have to ask our driver how much run time he gets with our relatively light and simple robot in practice sessions before needing to recharge. I would guess that he has been getting at least 15-20 minutes.
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Not in FRC (or most other) usage.
Rarely, but some batteries can theoretically be used forever especially with proper maintenance.
This assumes a very wide definition of battery, the definition used here is âstores energy in a form that can easily be converted to electricityâ.
Examples of such batteries that might last forever include lifting a brick - as long as you make sure nothing breaks, it wonât lose energy and youâll still have the full capacity.
However, thatâs not true for most batteries, especially anything small enough to fit something portable (Car scale or something, not like container ship scale)
Most batteries youâre gonna see called âbatteryâ use chemical energy to produce electrical energy. Itâs really hard to make sure no chemical energy is converted to electrical when you donât want it (and is theoretically near impossible). The next best thing is to minimize it. This means any chemical battery (and most non chemical batteries, too) will degrade over time.
Iâll go back to the brick concept for a moment. Losing charge is like the brakes that keep the brick in place canât keep the brick in place, so the brick will descend at a certain rate over time. We want that rate to be as low as possible, but with repeated usage, that rate tends to increase over time. This is why you see ârated charge cyclesâ on basically any rechargeable battery, such as the SLA motorcycle batteries FRC uses, or your phone/laptop/tabletâs lithium battery. Thatâs how many times the manufacturer has designed the battery to keep above a certain charge. Lithium batteries tend to be rated for many thousands or more cycles, while SLA batteries generally have a much lower rating.
Long story short, the reason why this happens is essentially that you canât get 100% of the charge you put in back, even if the charger were 100% efficient - some of the ions canât make it back to where they started, and this is why charge cycles exist. There are a few very sketchy ways to increase this but theyâre not particularly safe or require specialized equipment.
FRC uses what are essentially motorcycle batteries - relatively large lead acid based batteries originally made to provide a motorcycle with the power to start the engine (aka a very large amount of energy very quickly). They were not designed to power a FRC robot, and FRC is insanely demanding of these batteries as a result. Normally, these batteries are rated for a few thousand/10 thousand cycles, but FRC usage brings that down to something like 400, which is a few seasons at most, with driver practice. (Please correct me if Iâm wrong, Iâm pulling these numbers out of a notoriously sketchy memory) FRC usage draws a truly insane amount of power, very deeply discharging the battery, which is really really bad for the battery and significantly lowers the lifetime, at least in lead acid batteries.
If youâre looking to calculate the lifetime of a battery, any halfway decent manufacturer will have some form of information on this - Apple, for example, rates all its batteries for a certain number of charge cycles. FRC, however, does not use batteries in the intended way, and in general these batteries are gonna last like 400 cycles for an average team, depending on a range of variables. Iâve seen pretty functional batteries in 2019/2020 from 2012, but Iâve also seen batteries that barely lasted a year. The best way is just to test the battery every so often and use the newest batteries for competition and use other batteries for practice, where a brownout doesnât potentially cost a large amount of money or time.
After enough charge discharge cycles you can keep using them, not as effective batteries but as door stops or paper weights.
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The FRC arms race that brought us Falcon 500s and COTS swerve drive is making life difficult for our batteries (only speaking for team 230, YMMV). I keep a pretty close eye on our batteries. Most are no longer good for competition after 40 discharge/charge cycles.
We generally buy new batteries for comp ever year, use the previous years comp batteries for outreach, demos and practice matches, then the third year we recycle them or donate them.
We test our batteries at the start of each season to rank them for competition or for outreach/practice purposes. Surprisingly we have some older batteries that still are competition capable. And some new ones that are not that great. We use this product: CBA V - Computerized Battery Analyzer - West Mountain Radio
[edit] (found a photo) Be sure to label your batteries. Normally there would be either a red âCOMPâ label or a yellow âOutreachâ label on here as well, but this one is destined for recycling.
{aside} every year the students pick a theme for naming that yearâs new batteries (cheeses, pokemons, my little ponies, etc)
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If you go this route, Iâm a fan of continually replacing part of the set every year. We maintain 8 competition batteries, and have traditionally introduced 3 new batteries every season (though itâs been 4 recently). By buying a few every year, it keeps costs more predictable, and if thereâs a battery thatâs degrading faster than the others, itâs easier to replace it quickly (not only because youâllLimelight, an integrated vision coprocessor have more the next season, but we find the âbestâ of the batteries cycled out of use each season is generally still above our competition standards and could be returned to the rotation if required).
FRCFIRST Robotics Competition batteries wonât even last 100 cycles at peak performance. I budget a minimum of 6 new batteries each year for competition. Last yearâs batteries get used for practice. Some teams buy more.
To maximize your battery life:
- Swap your batteries as soon as you start getting brownouts. Lower depth of discharge = way more cycles
Thatâs pretty much it. Thereâs other stuff that you could do but thatâs the 1 thing.
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Luckily, they donât have to. Typically, they only get 1 or 2 uses per competition day. So for us thatâs maybe 10 or so uses per year (for our comp batteries).
General disclaimer but live within your teams means. Batteries ainât cheap.
That said, 6-8 new a year has worked for us. We held off using brand new batteries during drive practice until about week 0. We have run significantly more drive practice this year so we were limping though with our 2023 batteries for our last off-season this past week.
For drive practices, we still run 2022 and even a 2021 battery to â saveâ competition batteries. I have little technical background on the matter but use qualitative data from our drive team to sort through our stockpile. Anything much older than that hasnât held up for a full match in our shop.
Important note I could have skimmed over in the thread but you can recycle old batteries.
In the past, we have recycled them on a free electronic waste day our high school held.
We also made a couple bucks ($10 per x 5 batteries per visit?) at OâReilly Auto Parts. Itâs been a year or two but I think they still accept these.
A lot of companies will pay pretty good money for old batteries that are pretty much useless to you.
One of the nice things about SLA batteries is that theyâre really easy to recycle.
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What places have you found that pay for old batteries. Some auto parts stores will give store credit but it is is inconsistent, depending on the person in the store.