Battery dying at high percentage

how long have you been useing this battery?
if you have been useing it for a long time then the rechargeing might have depleated the batterys life because you can only recharge a battery so many times before it dosnt charge at all

On the Vex website, and the link for the battery it shows that the battery can use up to 2000 charge cycles

can you run the medic on the robot and see what it shows in the few seconds before the battery turns off. Pay special attention to the voltage of the cells, do any drop below 2.6V ? Are you driving the robot when it turns off ? does it happen without running motors ?

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This is the first year we are using this battery. We are at 51 charging cycles.


That’s what we got right before it turned off. What was happening at first was I would start up the robot and wait for it to connect, then using the controller startup the code to practice. By the time I had started the code the controller would say “Robot Link Lost” and then this would happen.

the forth cell of the battery might be damaged, thus stated by the fourth cell being a lower voltage

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also, does this happen with all of your batteries or just this one?

I can’t really tell much from that because the charger is plugged in. I need to see what happens before the battery turns off. Hopefully you are not running the robot with charger plugged in.

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It is happening with specifically this battery. We have another one that is not doing this.

I think your problem is in the fourth cell of the battery. look for a dent/scratch/or the plastic wearing. that would be the fourth cell. if you have a replacement for that battery I would suggest taping a note to that place on the battery and sending it back to vex so that they can send you a new one and investigate why the cell got damaged.

Ill look into it. Thanks

no problem

Minor physical damage to the outer casing like @JamesChase suggests would almost certainly do absolutely nothing to the internal circuitry and function of the battery.

If external physical damage actually did something to your battery, I can almost guarantee you would not need to look for it.

Instead, what is significantly more likely is that you just got a defective cell from the factory. This is what @jpearman is trying to help you diagnose.

@jpearman has been one of the brains behind VEX software and firmware for many years, and he knows what he is talking about.

I suggest you do as @jpearman suggests: run the battery medic on the robot without the charger plugged in, and see what the cell voltages are in the seconds before the robot turns off.

Also, the fourth cell being at 3.22 V while the others are at 3.30 V is not really significant. You cannot draw any conclusions based on that alone.


I just figured that since the battery was not at full it was just that one of the cells was partially drained. I will be running battery medic and recording the whole process on Thursday when we have a meeting. Thank you!

(Helping out a sister team here) The charger being plugged in was our guaranteed way of making sure the brain would actually turn on and allow us to run battery medic, sometimes the battery would outright fail to power the brain when it wasn’t plugged in (though that most likely didn’t help us) There were motors/radio plugged in, but no code running or any active attempts to power the motors. We’ll run battery medic with the battery not charging Thursday first thing. And this one’s for the coach/other team members - pressing the reset button is NOT the way to go, correct?

yea, don’t press the reset button.
My assumption here is that there is one bad cell in that battery, but we need the data to prove it.


yea, please don’t do that, I specifically said don’t press the reset button in the previous post.

Here is the battery medic display while the battery is not charging.

and there’s the problem.
Cell 4 is not holding charge, that’s the source of all the under volt errors.
that battery is probably not recoverable at this point.


Alright. Thank you for you help