Can you revive a dead battery?

Electrically assisted bikes, trikes, etc.
hercule
Posts: 939
Joined: 5 Feb 2011, 5:18pm

Can you revive a dead battery?

Postby hercule » 20 Apr 2019, 4:59pm

A couple of years ago I added electric assist to one of our recumbent trikes so that my OH could get out a ride with me. It took a lot of fiddling but I finally got there! Sadly last year I only managed to persuade her to get out on it once, but she’s been talking about using it again, so I was full of hope!

I’ve used the trike myself since converting it, it’s done a few 20 mile rides but not much over the winter. Aware of the dangers of “deep discharge” I’ve perodically kept an eye on the battery charge and given it a top up every now and then.

Took it out yesterday and turned it on... to be greeted with nothing. There’s an LED rear light on the back of the battery (it’s supposed to mount under the saddle) and it won’t come on, the charge state LEDs are similarly dead. Looking at it more closely today I’ve spotted two fuse holders and will check them before doing anything else, but I suspect the battery is currently an ex-battery.

Is there any way of resuscitating it or am I looking at a replacement battery? I’ve seen YouTube videos suggesting briefly connecting a similar voltage battery in parallel but the only thing I’ve got is a Kalkhoff battery that I don’t want to risk!

kwackers
Posts: 13067
Joined: 4 Jun 2008, 9:29pm
Location: Warrington

Re: Can you revive a dead battery?

Postby kwackers » 20 Apr 2019, 6:11pm

I'd get a multimeter and make sure it really is the battery.
I'd even open up the battery case and check the voltage before the BMS before writing it off.

If the charger won't charge it up connecting another battery alongside won't either since likely the BMS sees the low battery voltage, sees it as a fault and inhibits charging regardless of the source.

I have in the past taken the case off batteries and applied a current controlled charging source directly to the batteries for a few minutes (before the BMS) with mixed results depending on whether there's a dead cell or the batteries are OK but just over discharged.

If you have one or more dead cells then you'll need to identify and replace them and if the battery appears dead it's quite likely this is what you have.
You might have to take it to someone with the ability to identify, test and replace the dodgy cell(s).

hemo
Posts: 360
Joined: 16 Nov 2017, 5:40pm
Location: West Sussex

Re: Can you revive a dead battery?

Postby hemo » 20 Apr 2019, 10:44pm

Measure the battery voltage at the discharge pins first to see what voltage you have and also check the chargers output voltage.

If the fuses check out ok then there are a couple of reasons why a pack will not charge.
If a cell group voltage is low usually below 3.2v then the BMS will not allow charging to begin until any low voltage is raised above it.
Also if any cell group is still fully charged (4.15 - 4.2v) again the BMS will not allow charging to begin.

If there is an issue then the only real way of knowing what the problem is is to open the battery and carrying out some basic voltage checks of the cell groups via the sense wires connected to the BMS.


Opening and closing a battery is the hard part, if you want to carry out some basic/simple checks come back for some guidance.

Checking each cell group will determine where any issue may lie and dosen't always mean the battery is toast, as long as no cell group is below 2.5v.