Is it possible to use a single battery for an extended period and recharge it as required? Additionally, how can I determine or calculate the expected lifespan of batteries? What strategies can be employed to optimize battery usage? Appreciate your assistance in advance!
Im not super knowledgeable, but my team tends to replace batteries every season. Some batteries survive a second season if their resistance isnt too high. Do note however, that oir batteries went through 10 competitions this season and 9 last season, so we probably run through batteries faster than other teams might. I know one thing you can do to extend your battery lifespan is to not overuse it. If your robot starts browning out, take that battery out and begin recharging it. A single battery will probably not last you more than 1 match unless you are running a small amount of motors or other power consuming electronics.
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Current limits 99% of the time will prevent you from browning out, but your batteries over time will get to the point where you need to drop them to 30amps to not brown out. At that point, it’s time to retire the battery. A more empirical way to determine if a battery is good is to use the computerized battery analyzer and perform a discharge test.
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Internal Impedance, but seems to go by resistance on this forum.
Never the less:
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How significant of an effect do you think the internal capacitance and inductance of an aging battery is compared to its internal resistance?
You seem to be inferring that folks are mistakenly referring to the wrong measurement criteria, but the other components of impedance are typically more relevant in an AC circuit, or I suppose one where you consider or rely on backdrive to charge the battery and influence its performance. Battery beaks specifically measure resistance (not impedance) and I’d think a brownout condition in a DC circuit would exhibit negligible instantaneous capacitance/inductance…
Not much unless some weird situations are occurring TBH (cold batteries vs warm for example). I am saying that resistance is technically incorrect in this case, (this was news to me just a few years ago considering how commonly the term is thrown around). Having said all that, this is an educational program and and archive of knowledge so a few links back to the “textbook” vs “common” terminology can be useful.
You are definitely correct in the assertion of measurement device availability though, battery beaks measure resistance so it is far and away the more accessible metric .
The answer is: It depends.
A slightly more detailed/in depth explanation below:
Disclaimer: Not a battery expert, this is based off of my experience
To my knowledge, there are very few (if any) form of rechargeable battery, including the batteries in your phone or the batteries in your car/motorcycle/FRC robot/piston airplane, that do not lose capacity or degrade in some form over time. I’m even including gravity based water reservoir systems here, as those do need regular maintenance. If you’ve ever used a phone/laptop for 7+ years you almost certainly know this from experience.
FRC batteries lead a much harsher lifecycle than most batteries as they go through extremely deep discharges over a short period of time, which is not good for the battery. The longest running FRC battery I’ve seen was a battery from 2012 in 2020 - that thing had mistakenly been set into the “competition” rack and probably was the cause of multiple random electrical issues in one particular match.
However, as the batteries degrade, they still retain some capacity.
So, yes, they still hold charge. But not as well as they used to, and you probably shouldn’t use a 2012 battery on a competition match. However, I’d advise to keep a decent sized stock of older batteries on hand, as they’re still very useful for practice or those times a robot needs to be on but doesn’t need to be moving for the programmers to work on it. Saves some wear and tear on the good competition batteries, when you need all the performance you can get.
When you’re done with the batteries, most auto stores will take them back - lead acid batteries (the chemistry FRC batteries use) are really easy to recycle and you may get some money back from it.
The lead acid batteries used in FRC will inevitably degrade with time and use. However, they degrade faster at higher temperatures and if they sit around discharged. Storing your batteries in a room-temperature-ish environment and storing them fully charged should prolong their life at least a little. That being said, I’d echo other people who say to replace them regularly.
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We keep our batteries several years. We monitor the performance using a battery beak and testing with a battery analyzer. There is really not a hard line based on just age that a battery transitions to none competition use.
Battery resistance, or impedance if you like, is really just a way to model a complex chemical reaction that makes electricity. It is really a function of current flow and not a constant.
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