Left E-Bike battery all winter without charging

[LEAHROBINSON65]

Hi all!

I'm new here and definitely have no idea what I'm talking about, so I'll apologize from the start. I (very foolishly) didn't ride my e-bike all winter and forgot to charge the battery for at least 5 months. Currently the on-board battery reads that it is full, but when I put a multi-meter on it I see no charge coming out (please note that I am using my neighbors multi-meter from the 60's so it's not as easy to see exactly what current is coming out). From everything I've read, either the battery is completely toast, or it is so low/out of balance, that the BMS is preventing it from charging. I've also read that you can disassemble the pack and test the individual cells and trickle charge to get them even, but this seems WAY over my head. Does anybody have any different ideas? I'm trying to sell the bike as it's to haul one kid and we have another on the way, but it already feels a bit unbalanced so I'm getting something more in the cargo hauler range (God help me!), but I don't want to have to buy a new battery just to sell it, and I can't really prove that everything else is in good working order with out power to the engine. Just looking for some guidance! Thanks All!

Bike/Motor/Battery Stats: Felt 29er hardtail with BBS02, 48V 15amp rear rack LiOn battery

 

[amberwolf]

There are ways other than disassembly to recharge a battery that's gone too low...but without knowing first how far discharged the cells are, that can be dangerous (if they're really low, they can be damaged in a way that could leave them vulnerable to catching fire, etc--less of a risk with LiFePO4 but still present).

So I would recommend first checking some voltages.

Set the multimeter to DC Volts, and if it has ranges set it to something that can read above 60v.

Connect the red lead to the battery positive on either output to controller, or input from charger, whichever is easier for you to touch it to without shorting it to the battery negative.

Connect the black lead to the same connecotr but the negative contact.

Note down the voltage and post it here.

If you can do this on both charge and discharge connectors, it's even more helpful.


If the voltage reads very low (a couple dozen volts or less), then you'd want to open it up to check at the cells themselves to see if they've really been drained that low, or if it's just that the BMS has shutoff it's output to prevent charging cells that went lower than it's limit.

If the cells are really low (less than a volt each) then it may be better to replace the battery than to recharge it.

If the cells are not that bad, (a couple volts each, and all close to the same voltage), then you could try making an adapter to connect the charger to the *discharge* port instead of the charge port, just to see if it will start charging. If it does, you could let it charge for a few short minutes this way, and then retry it on the charge port, where it may be able to begin charging normally.


If it won't start when on the discharge port either, and/or all the cells are at nearly 3v, then the problem may be in the charger instead, or the connection / cable between charger and battery.


If you don't know where or how to set / connect / etc some or all of these things, then post good clear pics of exactly what you have (including the voltmeter) and we'll point out what you're looking for. When you post the pics, use the attachments tab below where you type the post, and upload them direclty to the forum, so that anyone that can see the post can see the pics.