Best way to charge batteries

Hey guys.

My team has been having a big problem with dying batteries. I’ll cut right to the chase - is there any benefit to charging the batteries more slowly?

We charge all of our batteries on the 6 amp setting. Even the one we got this year dies pretty quick. (They’re all Genesis batteries)

We’ve ordered some more batteries, but we need to know if the charger is going to cause the same problem.

Generally, you will want to charge at the lower rate.
Charging a battery at it’s max charge rate will lower it’s life.

I know my team has been eating up batteries like never before this year, but then again we did design a drive train that drew much more power. I guessing based on your question this isn’t the case for you guys, because this, naturally, makes a difference. Just trying to clear up the question for more discussion :slight_smile:

Yes, definitely. Charging the batteries slower prolong their life. Here are a few tips that I’ve been told over the years:

(1) Do not deep-cycle the batteries if possible. By “Deep Cycle”, I mean don’t drain the battery until it’s near-dead. Batteries don’t ever really fully-recover from being run until they’re basically dead, a couple of times of doing this and your battery will never get back to full charge. Fun Fact: Lithium Ion batteries like to explode if you completely drain them and then try to recharge them, so many batteries have a “suicide switch” in them that will prevent the battery from recharging if they get below a set level.

(2) Do not charge batteries while hot. It’s best to pull the battery off the robot and just set them aside INSTEAD of immediately putting them on the charger. Give the batteries about 30 minutes to cool, and then put them on charge. You’ll get a much better charge on the battery that way. Interesting fact: The difference between a fast charge (charging in 2-4 hours @ 6A or 10A) versus a slow charge (charging in 8-10 hours @ 2A) is heat and gas buildup. Charging a battery quicker causes the battery to heat up quicker while charging, which damages the battery. It can cause hydrogen gas to build up inside the battery and if the gas isn’t vented properly can cause a dangerous situation.

(3) If you think your batteries aren’t charging properly, check the voltage on the charger itself. It must be charging at a voltage higher than the battery itself in order for the battery to get a good charge. You can detect a dying battery charger by checking its charging voltage.

(4) Never trust the voltage off a recently-charged battery. If you merely test the voltage with a voltmeter, you will be seeing what’s known as a “surface charge”, you won’t actually know how “good” a battery really is. My team really likes a product known as a Battery Beak from Cross the Road Electronics. The bugger is $150, but well worth it. It tests the battery at various power draws, and can show you what the REAL level of the battery is.

(5) If your battery doesn’t seem to be charging properly and you’ve ruled out a bad charger, check the terminals going to the battery. I’ve seen WAY too many batteries that didn’t have a SOLID connection between the wires and the battery terminals, and that can lead to loss of power in charging. I’ve even seen the connection corroded (rust), that’s never good!

(6) Last but not least, never leave a battery on a charger unattended. I’ve been witness to too many batteries exploding while on charge. Fortunately none of them at FIRST events, but unfortunately the worse ones were at various robotics competitions (mainly BEST Robotics).

Happy Trails.

You should test the batteries to see if they’re shot.

The best way to do this is with a CBA tester. If your team is low-budget there are simple and inexpensive but manual home-brew ways to do the test.

The quickest way to kill an FRC battery (other than dropping it) is to discharge it too completely. The recommended depth of discharge is no greater than 50%. If stored improperly during the off-season, the battery will die a slow but inexorable death.

If the CBA is out of your price range, take your batteries to AutoZone (or similar auto parts store). They will usually test them for free and let you know if the battery is usable anymore, especially if you tell them what you are doing.

Not. Autozone does a short-duration high-load test. This does not reliably test the battery capacity, and may damage the battery if done improperly.

No it will not damage the battery as it does not apply as much load as the typical FRC drive train and it does so for a much shorter duration.

“It” depends on the load tester and who is operating it.

Generally, AutoZone uses a conductance tester such as a Midtronics, and not like a carbon pile of the olden days. In other words, a LOT like the battery beak. These are very fast, lightweight, and accurate, and do not rely upon the user’s skill.

Thhat being said, even a 150A load for 10 seconds will NOT damage an FRC battery. It’s not good for this to be done on a regular basis, but 2 or 3 times a year is not harmful.

We always charge at 2amp unless we are doing a demonstration where we know we will drain enough batteries to have to reuse them quickly.

I’ve posted this before and I’m not sure if it’s still true, but we were able to get West Mountain to send us an old CBA III for free just by telling them it was for a high school project.

The CBA and Battery Beak allow for you to actually know you have good batteries. Also make sure you have good contacts at the battery terminals, Al recommends star washers between the ring terminal and batter lug and we have been using them with great success the last few seasons. They don’t let the connection come loose. Also common sense, never carry or lift a battery by it’s leads.

Check the SB50 connections them selves, they can get damaged and hinder battery performance.

They may be accurate for what they do. But they do not measure the battery’s capacity.

I have an old battery in my shed that passes with flying colors when tested with my “125 amps for 10 seconds” tester. But it fails miserably when subjected to a capacity test. So even if the high-load-short-duration test doesn’t harm the battery, it doesn’t really tell you what the true health of the battery is.

even a 150A load for 10 seconds will NOT damage an FRC battery. It’s not good for this to be done on a regular basis, but 2 or 3 times a year is not harmful.

Yuasa NP18-2 datasheet: Maximum discharge: 112 amps.

MK ES17-12 datasheet: Maximum discharge current for 30 seconds: 360 amps.

Go figure.

We’ve been having some issues with batteries this season as well. We use the Battery Beak, check our batteries with the CBA before and after every regional, and try to conserve battery life as much as possible. What I’ve found, in doing this, is that batteries that are old, and especially have been dropped in any way, are noticeably less reliable, with less charging capacity and amp hours. We get around this by using brand-new (2013+) batteries, and removing them from the roster if they get dropped, until we can test them to find out if they’re usable.
After reading the OP, we charge all our batteries at around 3~3.5 amps. I’ll have my captain check me on this, but I do know that we don’t like to charge on the maximum amp. </EDIT>

How many regionals do you attend in a typical season?

Typically two, so at least: once before Utah, once after Utah, which is typically coupled with before Las Vegas. Then, if we’re lucky, after Las Vegas/ before Saint Louis, or if we’re not so lucky, then after Las Vegas. At least 3 times, maybe 4~5 if we’re lucky.


We have a battery that tested as “good” with the Battery Beak and then minutes later dropped dead halfway though a semifinal match last weekend. Fortunately, it did not affect the outcome of the match.

Battery 6 is going to that farm for old batteries…

Thanks to everyone who pointed out the shortcomings of the Autozone test. My team uses a CBA, and I’ve just heard it recommended around the pits.

I personally like the CBA, but it really only measures ampacity via a low current draw, not real robot loads. It has the amplifiers, but those are out of the price range of most teams.

Does anyone have recommendations on a good way for a team to do their own controlled 150A discharge test? Even the Beak only does an 18A load test.

Spend the $20 bucks on a load tester at Harbor Freight. That is the closest you’ll come to finding out how your battery performs with robot like loading. Yes that is a 100a unit but you can find 125a and 150a units too, but will likely pay much more since you’ll have to go someplace other than Harbor Freight.

The CBA might be great for testing the battery against its designed usage but we don’t use the battery anywhere near that discharge rate. The Beak is a great way to test the SOC and internal resistance but that only tells part of the picture.

How do you recommend hitching an FRC battery to that load tester, Mr V? Using clips to grab inside the battery’s anderson connector is discouraged due to the scarring it can do on the faces of the terminals inside them.

Thanks for the tool link, I’ll have to pick one up for the team. I think your point about these all telling part of the picture is most important here. Being able to test all the aspects of your batteries is very important, especially with how much we rely on them.

A beginner team should be ok with using new batteries and a multimeter along with the driver station debug plots to evaluate battery health, but getting more advanced tools should be a priority for their second season. As you start to develop an arsenal of batteries, with some being several years old, proper care and testing to evaluate worthiness before regionals is critical. Combining good charging and storage with proper evaluation can really set your mind at ease about this when you’re rushing to the next qual match.

Bill_B, I would just replace those jumper cables with an Anderson SBS (the big one on the batteries). It might not be a bad idea to put a breaker in line either. Then you just plug in the battery, and flip the switch to connect it. At the push of a button the test stops.