Robot Battery Maximum Voltage

What should be the optimal battery voltage for a competition match? My team’s chargers charge them up to 13.2v but i believe that some teams charge their batteries up to 14.5v. We use the chargers that came from 2021 first choice.
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Here is a good article on battery basics

I have never seen a battery register anywhere near 14.5 on FMS. Just above 13 is fine. There are a lot more important metrics however as the article describes.

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The charger you have pictured that they give out in rookie kits is, for lack of better words, a nightmare and a high priority of any team starting out should be to get a better battery charger. That charger is actually illegal per the rules as shipped, it needs to have an SB50 connector on it to be competition legal anyway. Most teams use this 3 bay charger from Andymark which charges batteries at 6A and is all around a pretty solid option. Now as far as battery voltage goes, how were you measuring your battery voltage? 14.5V for an FRC battery seems really high, I would expect a relatively new battery to sit right above 13V without a load on it, so yours doesn’t seem too low. Float voltage (or the measured voltage of a battery without anything drawing power attached) can be a little misleading, as what’s most important is the capacity of the battery (older battery, worse capacity, worse robot performance in a match).

Some other (very optional) helpful things:
Battery Beak - Measures pack V and general battery health, great for checking packs before matches

Battery Analyzer - Way more in depth of a battery tester (and therefore more expensive) but this device will actually plot your batteries capacity/time so you can tell exactly how well it’s doing. Not a necessary buy for teams, but it can be helpful

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I would expect to see 14.5 volts while the battery is charging…then when you disconnect the charger, the voltage in the battery quickly tapers off to 13.2, and if you let it sit for a day, it might drop further.

Maybe you are a bit confused about what is really happening with the battery voltage?

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The 14.5V (it’s more accurate to say 14ish) number comes from charging algorithms of “smart chargers”. That’s the magic voltage level of which you watch the current fall and you know you’re at the end of absorption then they jump to float or to open. A really healthy (chemically speaking) battery, sitting at rest should be just below 13V. 12.7V-12.9V is the natural voltage potential of a typical lead acid. We monitor both current and voltage during charge but that is mostly an OCD issue with us. I got to know where the electrons are going! The green light on most reputable chargers is the judge and jury most of the time.

This thread will end up with a lot of recommended chargers listed and they will all be good and FRC legal. We currently use a NoCo charger that appears to be discontinued. We also use the Andymark charger but we just watch the green light with that one.

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You should try and match what the manufacture’s spec is for the battery. You will gain a different experience depending on your charger. There are tons of lead-acid chargers out there and a lot of them have their own special sauce. There is defiantly an advantage to a lead-acid charger that uses a higher voltage, especially when charging in between matches. ES17-12

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These voltages are just charge voltage. I would not expect the battery to be at those votlages when taken off the charger. Like others have said it should be around 13.2-13.5 right off the charger.

Here are some examples of the variations in chargers.
https://earthxbatteries.com/our-batteries/battery-charging

Key things to note:

  • de-sulfate mode/deep conditioning mode/pulse mode voltage
  • maintenance mode/float charge voltage
  • Charge current
  • Charge Voltage

I would just use what a team you trust recommends.

Here are some FRC files i found in a quick google search:
771 Best Battery Practices (2011)

List of battery chargers

Old post on the Subject

Thanks for all the repliles,
As I understand from all of the replies I think it is tottaly normal for battery to be at that voltage. Also, we crimped sb50 connectors to the chargers. Since my team is in Turkey we don’t have any suuplier that sells those fancy chargers. I believe that best choice for us to use this charger. We have 4 chargers and planning to make a battery cart with them. I hope that it will not be a fire hazzard since they are not high quality.

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These batteries are composed of several cells (typically 6 for FRC batteries), in series. Each cell has a voltage which has to do with the electrochemistry of the materials. If you apply too high a voltage, “Overcharging with high charging voltages generates oxygen and hydrogen gas by electrolysis of water, which bubbles out and is lost. The design of some types of lead-acid battery allows the electrolyte level to be inspected and topped up with pure water to replace any that has been lost this way.” (Source Wikipedia)

You can measure the open-circuit voltage (no current is flowing, only a tiny amount used for taking the measurement). A good battery charger does this, and also monitors charging current and uses both of these to manage charging. The exact values to look for really depend on the specifications for the specific battery you are using. These values can also tell you something about the state of the battery.

Generally, the chargers marketed for FRC use are pretty good choices, if you can get the same thing, even if this is without the SB50 connector (which is easy enough to add).