V5 Batteries won't charged, never used!

Last April I ordered the V5 upgrades via PLTW. We’ve finally gotten to the point where we are able to use our “new” Vex Stuff. I’ve plugged in the V5 batteries and they seem to be dead. 2 of them never show anything except 1 red light (not flashing). The other 2 will charge to 1 green light and nothing more. I was able to hooked 3 of them up and run the battery medic on them. All cells are showing green.

HELP! It seems ridiculous I need to drop another $280 on batteries when we haven’t used them once yet.

HI if these are brand new, a call to VEX support should be able to get warrantee replacement.

There are battery trouble shooting articles in kb.vex.com in the Trouble Shooting tab:

The Cells do appear fully charged.

Hi, not sure what the issue is but this here is a link of types of battery error codes hope this helps!

I would recommend resetting the batteries by pressing the small reset button on the battery
Not sure if that will fix the issue though.


Put them through a couple of full charge/discharge cycles and see how they react after that, they may need to relearn capacity after sitting unused for so long. Once they are behaving better, be sure to update all firmware (update the brain to V1.1.0) as medic is also showing battery firmware is out of date.


No, no. Please don’t do this, that’s exactly the type of thing that will cause displayed capacity to become unsynchronized with reality.


Here’s my best guess: the question had been answered by J Pearman, an expert, and it was marked as the solution. No further posts are really warranted, especially non-helpful ones, but then you posted “DO IT ANYWAY” so somebody flagged it as bad advice.


Alrighty then
(And yes i see the jk but still)
Listen to boss man JPearman and it’ll be Bueno.

This would be a great sign to lay low of posting on a specific topic or completely avoiding it since there is always a great reason why stuff is flagged.


For the sake of being accurate… Lithium based rechargeable cells are fully charged around 4.2 volts per cell unless I’m missing something.

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V5 batteries use LiFePO4 chemistry.
Typical fully charged cells will be 3.6V, the charging circuit will consider charge complete when pack voltage is 14.4V and current drops below some number that I don’t remember just now. If the pack is not balanced, we do allow cells to go to 4.1V (IIRC) at which point we may trigger over voltage fault if the balancing logic doesn’t cause that to drop. However, once charging stops, cell voltage will drop quite quickly to 3.2-3.3V per cell.


Sounds like we are talking about the same cell chemistry, but y’all are being a little conservative with your charging parameters.

Some interesting reading here… there batteries have been in development a LOT longer than we realize, and a couple of guys actually won a nobel prize for work in this field.

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Not exactly. These batteries are lithium iron phosphate, which is a type of lithium ion. LiFePO4 have a lower power density and voltage, but much higher lifetime and safety and tend to be cheaper.


Ok, got it. But I thought the v5 pack was around 15-18v… contributing to my tendency to think the cells were a higher voltage.

The nominal voltage is 12.8 volts

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