Help! Bought a used ebike with battery/BMS issues..

[WheatyPop]

Recently I bought a used Velowave Ranger ebike, and I have spent quite a bit of time fixing it up. I finally had it up and running, but I discovered a pretty severe issue with the battery.

The battery works fine during pedal assist 1 and 2, but if I go any higher, the battery will shut off and not turn back on. Full throttle has the same effect. After I plug the battery into the wall, it will turn on again. This seems to be a problem with a weak or unbalanced battery pack - I just don't know how to fix it.

I'm currently trying a long top-balancing session to balance the cells in the battery. I'm not much of a tech guy so any help or assistance is appreciated. thank you

 

[spokewrench]

That happened to me because a bike had sat too many weeks or months. I plugged a watt meter into the wall, a timer into the watt meter, and the charger into the timer. (Watt meters and timers can be under $10 these days.) The watt meter gave me an idea of how much charging was going on at the moment. The timer was to be sure it didn't continue to charge when I was away. I'd charge it in increments of an hour or two. It worked out well.

 

[Chazmo]

Just to add to what @spokewrench said, please be careful if you do this to try to revive and balance the cells. Do this in a place that’s away from combustible materials. If a battery has a weak cell, there can be several reasons for that, some of which may not be repairable by recharging.

If a lot of heat is being generated with your charger on you might want to be circumspect. Do you know anything about the history of the bike? Good luck!

 

[WheatyPop]

@spokewrench My bike has also been sitting for quite a few months, and this could be a similar issue. Do you think you could elaborate on what I need to do and look for when using the watt meter and timer? The battery is sitting at 100% currently also. Thanks for the help

 

[Gionnirocket]

If it's at 100% then it has no problems. How are you determining this?
I would read the voltage at the output terminals to better understand it's condition.
If it does have storage related issues you may be able to coax it back to reassemble health by slow charging. I doubt very much that your BMS has the ability to balance charge.
Also don't leave it at 100% as that is harmful to battery health as well. Store your battery at approximately 50% and charge it to the desired level before riding.