Hi all,

I don't use my e-bike very often. However I do still charge the battery every now and then. I last used the bike a couple of months ago and the battery seemed strong and working well.

A few days ago I put the battery on the charger and left it in the garage. I returned to it some hours later and the light on the charger had turned green. All looked normal. But when I switched on the power to the bike (from the button on the led panel on the handlebars), it was completely dead. I removed the battery from the bike.

It's a 36V battery. I measured its voltage at the battery +/- terminals, and weirdly it showed an output of about 0.25V. Flipping the on/off switch on the battery casing made no difference. I also measured the voltage being output by the charger and that seemed fine, at around 42V.

I researched on the web, and found several sites/posts mentioning that the battery could need "re-balancing".

After more reading around, I opened up the battery casing and measured the voltage of each of the groups of cells. There are 30 individual cells inside the case, arranged in 10 groups I believe. Each group was giving between 4.06V and 4.09V, except for one group which was at 4.29V.

I don't know if that was high enough to cause the BMS to prevent any further charging. But I tried to re-balance the battery by partly discharging the group with the highest voltage. As suggested on another post here, I did this by connecting a 12V car bulb to it for about an hour. This brought its voltage down to 4.09V, so it was now in line with all the other groups.

But the voltage being output by the whole battery is still unchanged at 0.25V. I connected it to the charger and it seemed like it was charging up and after 20 minutes the charger showed the green light. But there was no change to the battery output voltage. I tested the operation of the on/off switch in the battery casing, and that's working fine.

Now I am stuck. Maybe it's not just a "re-balancing" issue, but a deeper BMS problem. Does anybody have any ideas or suggestions that would help me diagnose, and if possible, fix the problem please?

Thanks

(This is a summary of my long post above.)

My 36V battery, appears to be dead, with negligible voltage output from the battery +/- terminals. But the individual cell groups within the battery casing all appear to be ok (each group is giving approx 4.09V).

The cell groups are not "out-of-balance", however the battery will not charge up. (The charger is working fine.)

When the charger is first connected to the battery, it looks like it's charging up, but the red light turns green after about 20 mins and the battery is still "dead".

Any assistance in diagnosing the issue would be much appreciated.

45 minutes ago, andrewio said:

(This is a summary of my long post above.)

My 36V battery, appears to be dead, with negligible voltage output from the battery +/- terminals. But the individual cell groups within the battery casing all appear to be ok (each group is giving approx 4.09V).

The cell groups are not "out-of-balance", however the battery will not charge up. (The charger is working fine.)

When the charger is first connected to the battery, it looks like it's charging up, but the red light turns green after about 20 mins and the battery is still "dead".

Any assistance in diagnosing the issue would be much appreciated.

Sorry, I missed your first post, which must be something to do with the new forum format.

Your problem might be as simple as a blown fuse. The first thing to check is whether the BMS has switched off the power. You do that by checking the voltage between the positive terminal and the point where the negative output is soldered to the BMS, which should be marked P-. If you have voltage there, it's a blow fuse or connection issue. If there's no voltage, then look at the battery's switch if it has one. Some have hidden switches that might also work the charge level indicator lights

If it's neither of those, we need a lot more details about what battery it is.

Edited April 22Apr 22 by D8veh