Is my battery ruined?

DIY Builds Battery Builds
#1

I just repaired a popped fuse in my build - Key accidentally shorted the XLR charging port :upside_down_face:

I didn’t realize that my single-motor FOCBOXes (FOCBOX minis?) would turn on every time something connected to Bluetooth in my apartment while I had them disconnected from the power button on my board. Even still, I just kind of assumed that they would turn off after a few minutes of idling. However, while my battery showed 44% when I took the thing apart, it sat for a while, and by the time I put the new fuse in it, it was at 0%. Below 0, maybe. The backlight on the LCD display wouldn’t even turn on. 30Q, 12S pack.

Regardless, with a 12S pack, I checked the voltage, and it read 33.6V. 2.8V per cell. I have a flashlight that uses a 30Q and it was discharged to 2.7V without any issues, and I see that the discharge cutoff is 2.5V. However, after charging it (the board) overnight, it only got to 29% before calling it “full,” and when I turned on the LCD, it dropped quickly down to 18%. That’s kinda normal, I guess, as it normally takes a few minutes to show the steady-state battery percentage, but normally it isn’t higher or lower than the initial reading by 11%.

I have a 12S 4A charger, and I see that when charging batteries that have been discharged significantly, you’re apparently supposed to charge them with a low amp rating? Shit… did I burn my battery? Was it not already toast in the first place?? I’m so lost. Is there a way to fix it, or should I give up my newfound hope and go back to browsing 30Qs and P42As?

Forgive me if this post is in the wrong section.

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#2

typical with diy. id get some iron cells and at least theyre more revivable next time. next time…

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#3

So it’s dead?

Also, iron cells? Do you mean those big packs BH sells?

#4

Also, I looked up Model 3 cells and found this site: https://www.techdirectclub.com/21700-lithium-ion-battery-18-5-wh-5000-mah-3-75v-model-3-2170-cells-lot-of-25/
Know anything about these guys? A lot of 100 cells is just $245…

#5

Don’t buy cheap cells and don’t buy used cells. These are both.

#6

tesla cells are not good for esk8

#7

This would leave me to believe one or more cells/groups are going bad or have gone bad.

Depending on how many cells/groups are bad, it might be worth dismantling it and finding the bad cells/groups. Could easily be two cells. Then again it could be a few groups. Wont know till you start inspecting it.

All else fails, buy something else.

#8

I’m leaning towards jumping ship, because I don’t really have the tools to take individual cells out, nor do I have the knowledge to feel comfortable deeming some cells as being fine and others not. Also, if I build a new battery, I can be much more certain that all my cells are at the same wear level. Regardless, there is no harm, per se, in tearing it down just to see/learn. Thanks

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#9

Those said skills are required to build as well. Same boat…

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#10

Cheap, sure, but all Model 3 cells have always been cheap, unless you buy from BigBattery.com ($6 a cell from them, whereas everyone else sold them at $2.50 a piece). How do you know they’re used? Just best guess? I don’t see it on the site I posted.

#11

They’re used, because Tesla doesn’t sell cells. They only come in the car batteries.

#12

But Tesla only sells cells (ha) which are in “defective” packs, which is due to mechanical errors in the assembly of the pack (incorrect bolt pattern, dinged panel, etc), which are tested and verified to be 100% before liquidation. I would trust them, if not for techdirectclub seeming to have not a single mention on these forums, from my quick search.

Regardless, if they’re rated at 15A continuous max, then they probably can do 8-9A continuous in reality without compromising usable lifespan, which is still low. For a range-oriented, relatively low-speed build, maybe…

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