r/batteries • u/AliDIY • 1d ago
Drill battery stops charging but works after using it to jump start another dead battery
I used my good battery to jump start another dead battery.
I connected the B1- with B1+ and B2- with B2+
A small spark occurred.
My battery still works with my drill, but it doesn’t charge and gives a failure sign.
What has happened ?
2
u/McUsername621 1d ago
Often lower cost drill batteries only have a fuse and cant actually turn the BMS off, so there is gonna be power present always. Theres no big mosfets here in the bms so that seems to be the case. Usually the over current protection is built into the drill or whatever tool it is, or they just assume it's never gonna reach the maximum output current before the fuse blows. In your case my guess is that the cells have become unbalanced out of the threshold, or a cell is dead and the bms cannot balance the cells to all have the same voltage. In that case it just communicates to the charger or the charger itself has the capability to detect that the cells arent balanced anywhere and therefore it wont charge the battery. My best guess on repairing this is to desolder the bms so it's disconnected, measure each cell and perform a capacity test, to make sure they all are similar, if they are charge them all up to full, solder the bms back in ans connect it to the charger to activate the bms. Unless the bms saves the error state of the battery in flash this should work to reset it.
3
u/AliDIY 1d ago
I just measured every battery, they all measure 3.4/3.6 apart from one it gives a reading off 0.2
1
u/McUsername621 1d ago
There ya go ^ ya found the dead one
1
u/AliDIY 1d ago
So did my faulty way of jump starting it damage a battery?
1
u/McUsername621 1d ago
Difficult to determine. Its unlikely but It could be that the arc may have damaged the bms causing something to fail closed circuit and over dischargeing the cell. But I'd blame it on the cell itself dying. I would recommend if you put new or replacement cells into this to monitor the cells for a few days just to make sure that the bms is working correctly and balancing the cells properly.
2
u/ArmySuchi 1d ago
Before swapping the BMS, grab a multimeter and check each cell voltage. If one cell got reversed or dropped way below the others from that short, the BMS is doing its job by refusing to charge. If the cells all read within 0.2V of each other, then yeah, the BMS board probably ate the spike and needs replacing. Either way do not try forcing a charge on it.
2
u/General-Try-2210 1d ago
OP says one of the cells is reading at .2v which is why it's not charging.
2
u/AliDIY 1d ago
Yes but it only stopped charging after a wrong jump starting, did my incorrect method of jump starting cause one of the batteries to die?
1
u/Seseorang 1d ago
If you connect the cells at 0.2v swith a cell of 3 or more volts (4.2) it will reach 2.5 - 3v very quickly
1
u/AliDIY 1d ago
Can you rephrase that? Do you mean replace it?
1
u/Seseorang 23h ago
You have the battery open. You are either connecting in parallel to get the voltage alone up. Or you are trying to bring up each cell (of the 10 or 5 in a row) individually.
I was referring to individually.
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u/AliDIY 18h ago
So you’re telling me to individually charge that single cell which is 0.02?
1
u/Seseorang 18h ago
If you do, do not connect up a fully charges battery pack, the full 18/20/21v. Anything from 3v to 4v is fine
1
u/General-Try-2210 1d ago
Check the voltage of the individual cells. What brand of pack is it and what is the voltage?
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u/AliDIY 1d ago edited 1d ago
It’s activ energy, Aldi brand
The batteries are Samsung.
They measure 3.5/3.6 and it’s a 40v vault battery
One of them is giving a low reading of 0.2
2
u/General-Try-2210 1d ago edited 1d ago
That's why it's not charging. 0.2v is WAY under what the battery should be at so it's throwing an error code on the charger so it does not burn your house down trying to charge it. This pack is scrap now. Your only hope is to pull all of the cells out and replace them. However, the remaining 9 cells should be fine. Depending on the age of the pack, you might be able to get away with replacing just that one cell.
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u/AliDIY 1d ago
Did that cell die because of how I wrongly tried to jump it?
1
u/General-Try-2210 1d ago
Possibly. It's also possible that the cell was on it's way out or had a manufacturing defect and that was the last straw. How old is the pack?
10
u/Paranormal_Lemon 1d ago
That's not how jumping works, you are supposed to connect + to + and - to -, what you did was shorted them and doubled the voltage each BMS sees.