Help diagnosing battery not turning off

I'm running into an issue where my battery will not turn off when I flip the switch while attached to the bike. However when I pull the battery off, open it up, and probe the switch itself, the switch seems to be correctly breaking and connecting the current. Now I'm stumped as to what could be causing my battery to be stuck in the on position, if anyone knows where I should even start?
https://imgur.com/rkPohKf

showing the switch working
https://imgur.com/7gyx6J4
https://imgur.com/svq9C93

can't see your pics. attach them to the post directly using the attachment tab, and then anyone that can see the post can see the pics.

fets in bms blown, fets typically fail shorted, leaving inputs and / or outputs stuck on.

also means it's no longer protected against overdischarge / overcharge.

probalby needs new bms.

Are the images working now? Which part of the battery would be the fets, and how should I check it to be sure?

theblindsaint said:

Are the images working now? Which part of the battery would be the fets, and how should I check it to be sure?

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yes, the images work now.

the fets are in the bms, which is the module with the aluminum panel(s) that's taped to the cell block package.

you may not be able to access the fets to test them without taking the bms apart, which may break things, or allow you to accidentally short things out which could cause other problems.

if you want to try testing them anyway, you'll need to post some good pics of both sides of the bms unit (without taking it apart, but you'll have to pull it away from the cell block as much as you can without putting undue tension on any wires, to see the other side of it). then we may be able to tell you where to put probes and on what setting.


fwiw, the fets rarely just fail; there is usually a cause.

so...what exactly and specifically happened just before this problem started?

The only other issue I've had with my e-bike was that sometimes the motor would not respond unless I turned the bike off and on again. Then one day when I tried turning off the battery it wasn't able to, and it has been that way ever since. What would be my best course of action at this point?

theblindsaint said:

The only other issue I've had with my e-bike was that sometimes the motor would not respond unless I turned the bike off and on again.

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does your bike have a display or lights or anything else that you can see is "on" when the system is on? if so, could you see that those were "on" when the motor would not respond? or were they "off" at the same time the motor would not respond, and did they then also come "on" when the motor began to respond?

if so, then that means the battery itself wasn't turning on correctly (or at all), so it might have been a precursor of this problem.

Then one day when I tried turning off the battery it wasn't able to, and it has been that way ever since. What would be my best course of action at this point?

Click to expand...

if you can't pull the bms away from the battery to take pics to let us point out where to measure anything, and you are sure the switch is working exactly as it is supposed to, then it sounds like your only option is to replace the bms to see if that fixes it. finding an identical bms is unlikely, but there are a number of threads around the forum about buying a new bms, and about others repairing their batteries that need new bmses, that have advice on which one to buy (that i don't have to give).


but before you do that, another thought:

do the wires to the switch go to a plug on the bms? or are they soldered on there?

if a plug, try unplugging it.

if no plug, then: can you solder reasonably well (and have the stuff to do it)? if so, you could try cutting one of the wires to the switch. doesn't matter which one, or where. the point is to cut the circuit the switch makes, completely, in case the switch has an internal problem allowing *just* enough leakage to keep the battery on, while still appearing to be working.

if the battery is still on even with the switch disconnected / unplugged, then the problem is in the bms.

if the battery is now off, then the problem is in the switch.