Warming up the batteries

I’m definitely not used to this problem, being a 5th generation Floridian. We have retrofitted last year’s robot to put a shovel in the ground and dig some dirt for the Ceremonial groundbreaking of a new high school in our team’s school district tomorrow morning. We did a test run yesterday and everything worked fine, except that the driver said it seemed to be running very slow. I checked the voltage of the freshly charged battery and it showed under 12V no load. Oh by the way, it was 17 degrees F outside when we made the test run, and although the batteries had been stored inside the school I had them in the back of the pickup for the half hour drive to the site.

It’s supposed to be up to about 50F tomorrow morning; If we warm up a fresh battery overnight and keep it warm until just before the big show, is it going to be good sitting for an hour during the speeches or do I need to wait until right before we power up to change it out?

Our drivers had a similar problem with the cold. I think it has to do with the physics of the battery.

The batteries are suppose to run at room temperature. That can mean different things. I would check the supplier’s website for specific temperatures that they list.

I’d wait until power-up, just to be safe.

I’ve seen what cold can do to a NiCad (admittedly not a lead-acid) battery at “warmer” temperatures of around 20 F–went from about 3-4V or so down to 2V or thereabouts in a matter of minutes. Yes, it was being used, but that kind of drop is peculiar. To make matters more fun, it went back up after I went inside for a couple of minutes. The lead-acid(?) 12V batteries were somewhat discharged already, but refused to work right until put inside and charged, so we grabbed a car to supply the power needed.

At 50 F, you might get away with it, but I’d keep it in the vehicle until right before you need it.

In other applications I’ve had good luck with a wrapping of a nice thick blanket and a handful of the chemical hand warmers.

I’m just waiting for either Ether or Al to chime in.

We had our 12v batteries running 201 and 245’s robots in a parade 2 weeks ago (Michigan suburbs north of detroit). It was freezing out and they had been sitting out all morning so they were at 32 F. The batteries tested at above 12v before packing (the warm school). While in the parade, they were slightly less but the robots ran the whole 30 minutes on 3 batteries.

The robots were sluggish, but nobody is going to question you changing the batteries before you start. I mean you need to take 5 min to turn it on anyway right?

I would not worry about 50 F weather. Its not their prime but it is alot closer the the optimal performance zone.

Based on experience using the FRC batteries in a previous robot we built, as long as you keep the batteries somewhere warm until a few minutes before they’re needed, you’ll be fine in 50F weather. The large quantity of lead in FRC batteries will maintain a sufficient core temperature until you start using them (after that point, heat from the chemical reaction usually keeps them warm enough to keep going).

If the temperature is closer to (or below) freezing, wrap the batteries in hand warmers and insulation.

We were involved (and organized) this event as well.

Using 2007 robot, without the drivetrain (1 FP, 2 Globe, 1 Banebots, and the compressor total), we ran on 3 low batteries (one was questionable, the other two were not fully charged but decent at 11.9-12v no load). All of the batteries were sitting on the truck with the robot for a few hours before the parade. The elbow joint (2x Globe) will not run on less than 11v, so we could deplete the batteries less than 201 and 245 could.

It was cold enough for one of our plastic rollers on the claw to break when closing. It was, however, very thin, due to extensive lightening efforts.

However, unlike 201 and 254 (which had cRio-based 2009 robots), our 2007 IFI robot could boot in under a second (on tether). We changed the battery during the parade without issue.

Without getting into the physics, “What Art Said” and you’ll be fine.

17F is hard on a lead-acid battery, and even harder on a gel cell. Less than half capacity.

I agree, Art hit the nail on the head. Just leave the battery on the floor of your truck until you need it. Don’t forget the lube in your robot is not made for low temps I bet and that will be as much of an issue.

FWIW think about it this way:

  1. All batteries produce energy and power through a chemical reaction.
  2. In order for a chemical reaction to occur atoms or molecules of the two reactants must interact.
  3. Temperature is the average kinetic energy (i.e. speed) of the random movements of atoms/molecules.
  4. When a battery is cold its molecules are moving slower than if it was warm.
  5. Slow moving molecules collide/interact less frequently with each other, making reaction rates in the battery go down.
  6. Slower reaction rates in the battery mean that the battery cannot produce electrons as fast as it could when warm, so it performs worse.

50F probably isn’t that big of a deal, but warmer is better.

Maybe some one here can help us. Our battery will drop from 12-13 volts to 9-8 in 1 minute of just being plugged in no matter what the temperature is. This happens with all of our batteries and we can’t figure out why. Temperature doesn’t affect it and neither does the amount of time that is charging. We have done research to solve our problem but have had no luck. We are afraid that we might have the same problem next year because we can fix it if we can’t diagnose it! Can anyone help? Thanks


I agree with all of the battery comments. You should be fine.

Two more aspects of cold ambient affecting FRC robots:

  1. The first is if your robot utilizes latex tubing. Latex changes its springlike properties dramatically at low temps.

  2. The second is to be sure that the ambient temp and/or robot temp is well above the dew point. The electronics, if cold, can condense moisture from the air and can make things interesting.




It sounds like you may have a faulty battery charger.



Or some part of your electrical system is damaged. Or the batteries are just getting old. Does this happen to every robot it’s plugged into or just one? How old are the batteries? Any idea how many charge cycles they have been through? Ever load-tested any of your batteries?

You have left a lot open to question. Does the battery drop with the robot turned on but not moving? It is normal for a battery to read 8-9 volts under load (while the robot is moving) after a minute of operation particularly if you are running the compressor and using a lot of air. When you stop moving and the compressor turns off, does the battery come back to 11-12 volts on your dashboard? Again this is normal.

If the battery draws down to 8-9 volts with nothing else running and stays there or gets worse, then you have a short or bad component on the robot. Start by pulling all the breakers and then putting them back in one at a time to determine which device is drawing the battery down.

We only have the one robot because we have to carry previous parts over to new robots. Could it be possible that all 7 of our battery chargers are bad? We have batteries dating back to 2006, but we have the one from every year. We haven’t load-tested it. How would I do that?

The battery drops just from the time we take it off charge, put it in the robot, and turn it on. It will drop to an unfunctionable 6ish by the end of a match. The compressor takes a lot, but our battery dies just by plugging the robot in and not even turning the robot on. At comps we plug in the battery then walk to the field and by the time we get connection it has already dropped from 12-9 and we can watch it drop by not even moving(without the compressor running)(and we’ll be disabled). But our volt meter will read something along the lines of 13 before it goes in the robot. And then once the voltage drops it does not come back up. We only had this problem during off-season competitions and practice this year, but never before that.

Thanks for your help!

It seems most likely that there is a problem with your robot’s electrical system. I would disconnect everything: the battery, main breaker, all the power distribution board breakers, etc. Measure battery voltage, connect ONE THING ONLY, measure battery voltage again, and repeat until you find out what component is draining your power.

If the battery is draining while just sitting there it may be a fault with the main breaker, Anderson connector, or all of your chargers/batteries were exposed to the same damaging conditions.

I’ll have to try it. Thank you so much!

Those symptoms suggest either that your robot is drawing significant current when it should not, or that something bad has happened to all of your batteries. Did they get frozen or baked at some point? (A frozen SLA battery will not have much capacity afterward, especially if it was discharged at the time.) Do you have one charger that has failed and keeps pumping current into fully-charged batteries? (We boiled a bunch of batteries that way a few years ago.) Does someone on your team have a habit of carrying them by the wires? (That is very bad.)

The possibility of faulty robot wiring is actually the preferable option here. Without a battery connected, use an ohmmeter to look for (and with luck, find) a connection between the power connector and the frame of the robot. Or you might just be getting physical contact between the battery terminals and some metal structure.