Batteries going bad after sitting

We are starting back up for this years upcoming robotics season. The last time we competed was at worlds back in the last part of April. Since then, our batteries have sat unplugged in our basement. Now, when we go to use them, they only last for 2 minutes at best. We have reset them, done all updates, let them fully charge/de-charge, etc. and nothing seems to help. Before we reach out to VEX customer service, I just wanted to touch base here on the forum. Any help would be appreciated.

We have about 8 batteries total that all have this same issue.

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Assuming you are referring to V5 batteries, you should never leave lithium-based rechargeable batteries fully charged for extended periods of time.

Instead, you should leave them at what is known as “storage voltage” — the optimal voltage for storing batteries for extended periods of time without use. This corresponds to about 40–60% state of charge for \text{LiFePO}_4 batteries like the V5 batteries.

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Please don’t keep reseting batteries.

were the batteries charged or discharged before being left ?

run the battery medic and post the results for one or two of them here.


Hello. This is 77000X personal account. They were not used from worlds to late august. The batteries were off the charger but they were all at 100% when we left them. When you use the battery now, a “full charge” will last only 2-3 minutes. Before we left them sitting, we were able to run one battery for 30-45 minutes with no problems. Any help will be greatly appreciated.

Be sure to run the Battery Medic like @jpearman asked you to. You only answered half of his request for information. James works for VEX and is your best bet at getting your batteries fixed, so be sure to answer all of his questions.


CD3455 is at school right now, but we will run the battery medic this weekend and report back.

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In addition, have a look at this

do the four green led flash when fully charged ?

what do the leds show after running on the robot for 2-3 minutes ?


How do we access or open the V5 firmware utility?
Is it in Vex Coding Studio?
Whenever we plug in our brain, the updates are automatically uploaded.

This is the firmware utility, although Vexcode automatically updates connected devices so there’s a chance you already have the latest version.

They need the standalone firmware utility for the Battery Medic, not necessarily to update firmware.

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we figured out how to download the firmware utility thanks to everyone’s help. Thank you for the help!

We charged 3 of the batteries up to full capacity, and then ran the battery medic on them. All of our firmware was up to date prior to doing this. As you can see from the pictures, all 4 of the cells have equal power. The only thing that we can see is that they all have multiple “under volt errors”. What are these? and can that be what is causing our issue?

We also paid attention to these batteries while charging, and they all went from 1-2 green lights on to 4 blinking lights when fully charged. We have not ran all 3 batteries yet, but the one battery that we did went from 4 green lights to 2 green lights after a normal 1:45 match run time. There was hardly any load on the battery while running. only 4 motors driving 4 wheels in a holonomic set up 200rpm.

the 4th battery in the picture we did not have time to charge, but it looks fine as well.

any ideas on why the batteries are not holding a charge would be appreciated! Again, thanks for everyone’s help!


Run the medic with a battery connected to the V5 and also on charge, make sure the full charge voltage is somewhere near 14.4V and all cell voltages are up near 3.6V. Run the battery on the robot until the V5 shuts off, check the battery with the medic again and make sure none of the cells are less than 2.5V. When you are driving, have a look at the battery dashboard and note the typical current, I would expect a 4 motor holonomic drive to be using less than perhaps 6A and should last for 15 minutes of driving.

If you used the reset button, the battery capacity (which controls the leds as well) may not sort itself out for a couple of full charge/discharge cycles. Using reset is generally not a good idea unless the battery is completely unresponsive.


Thanks. This will take some time to complete, so we will plan to do it this weekend when we have time.