Can you revive a dead battery?

Electrically assisted bikes, trikes, etc.
hercule
Posts: 970
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: 13801
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: 541
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.

KM2
Posts: 407
Joined: 23 Oct 2008, 5:38pm

Re: Can you revive a dead battery?

Postby KM2 » 4 Aug 2019, 10:47am

I was told, but obviously beware, that you could shock the battery back into charging by using a “higher voltage charger or high current “ . The person used a car charger having analysed the cells . 24v or 36v are multiples of the 12v car charger. I’d be very careful.

hemo
Posts: 541
Joined: 16 Nov 2017, 5:40pm
Location: West Sussex

Re: Can you revive a dead battery?

Postby hemo » 5 Aug 2019, 12:23am

KM2 wrote:I was told, but obviously beware, that you could shock the battery back into charging by using a “higher voltage charger or high current “ . The person used a car charger having analysed the cells . 24v or 36v are multiples of the 12v car charger. I’d be very careful.



Not going to work with lithium if a BMS is used/ connected, BMS is used to prevent over charge/discharge inc current. Though they can't prevent cells from failing if they have an inherent weakness.

Higher voltage or current will damage lithium cells that have a max current rating and voltage rating which is 4.2v per cell. Both will cause high heat thresholds which lithium cells don't tolerate well and will cause significant capacity loss.

KM2
Posts: 407
Joined: 23 Oct 2008, 5:38pm

Re: Can you revive a dead battery?

Postby KM2 » 5 Aug 2019, 1:16am

By shock them, I mean, switch on, switch off.

hemo
Posts: 541
Joined: 16 Nov 2017, 5:40pm
Location: West Sussex

Re: Can you revive a dead battery?

Postby hemo » 6 Aug 2019, 12:13am

If a lithium battery has a BMS fitted which most do then you can't shock them as they won't switch to allow current or voltage to pass.

KM2
Posts: 407
Joined: 23 Oct 2008, 5:38pm

Re: Can you revive a dead battery?

Postby KM2 » 6 Aug 2019, 2:06am

But you disconnect the electronics and deal with the bare battery, to shock it.

kwackers
Posts: 13801
Joined: 4 Jun 2008, 9:29pm
Location: Warrington

Re: Can you revive a dead battery?

Postby kwackers » 6 Aug 2019, 10:32am

In desperation I did do something similar to a drill battery that had one cell that was showing fairly low voltage and whose charger was refusing to cooperate simply showing 'fault' on the battery.

Once I'd identified the cell I stuck a constant current of about 250mA through it for 10 minutes by which time the cells voltage had climbed to a more sensible value, the charger was then happy and the battery is still in use.

I'm not sure I'd go for a less controlled 'shock' tactic though.
You could run the power through a suitable current sink to try and limit it - a 12v bulb for example.

If you do that you may not need to disconnect the electronics since the voltage shouldn't rise above the cell voltage.

atlas_shrugged
Posts: 270
Joined: 8 Nov 2016, 7:50pm

Re: Can you revive a dead battery?

Postby atlas_shrugged » 8 Aug 2019, 8:55am

If there is one battery segment that has a low voltage (e.g. less than 3.2V) then why does the BMS (Battery Management System) not allow trickle charging into just the segment with the low battery voltage (the BMS has connections to each of the battery segments) until it has reached a voltage above 3.2V. After this as long as no other segment is also low then main charging can be resumed.

OR

Is it the case that any lithium battery segment allowed to discharge below 3.2V can no longer be considered safe to charge and therefore the whole battery must be effectively scrapped for safety reasons. This by way of an executive decision by the BMS.

I have interest in this topic because the Mrs bought a secondhand Giant Twist eBike with two 26V Lithium batteries. After both batteries worked for a while. Both refused to charge at the same time during winter. Since then one battery and charger was sent off to a company that refurbishes batteries. A completely different charger and the original battery (possibly with new cells and internals) have been returned and an identical fault is present. The charger flicks momentarily to charging and then shows end of charge (i.e. open circuit). The output of the battery after 8 hours of charging reads 25.2V (it should be nearer 29.2) and when connected to the eBike shows one battery bar instead of 5. The eBike can make it 300 meters down the road with eAssist before indicating an empty charge and stopping eAssist.

hemo
Posts: 541
Joined: 16 Nov 2017, 5:40pm
Location: West Sussex

Re: Can you revive a dead battery?

Postby hemo » 8 Aug 2019, 10:22am

BMS is a safety feature though some do go wrong, it's main job is to prevent charging( HVC) and discharge(LVC) of lithium to a higher and lower threshold. If a cell or group goes below LVC then it will simply not allow charging, said cell group could have an inherent weakness or the BMS has an issue.
Under voltage cells/groups can be slowly bought up to other cell voltage levels by slow/low current charges usually of about 0.5a, shock charging is a no no with lithium and is used for other chem's like SLA or Nimh etc.
If a cell group responds to recovery charging then an eye needs to be kept on it's discharge,if the same cells /group go below LVC then either a single cell in the paralleel group has failed or the BMS bleed resistor has failed and remained in an open state, a new BMS may well be the answer once the cell group has been charged again.

hemo
Posts: 541
Joined: 16 Nov 2017, 5:40pm
Location: West Sussex

Re: Can you revive a dead battery?

Postby hemo » 8 Aug 2019, 10:27am

If the original cells and BMS were deemed ok and simply charged and returned then likely cells are aged passed their useful life.
If new cells were used and the original BMS then I would suspect the BMS is at fault. Though some batteries use a an internal charge fuse as do some chargers.
Though without opening and inspecting the battery you can't fault find, a low voltage could be a failure of a spot welded interconnector/s either on a parallel or series connection.
Not charging indicates a low voltage issue so again it is down to the BMS failing or a cell/connection issue or fuse if used.

Most capable people with common sense and a volt meter can to a degree take voltage reading to see where the issue lies when given guidance/instruction. There is little risk from probing contacts unless you allow the probes to short which then gives a momentary spark a reality check to be extra careful.

hemo
Posts: 541
Joined: 16 Nov 2017, 5:40pm
Location: West Sussex

Re: Can you revive a dead battery?

Postby hemo » 8 Aug 2019, 11:00pm

Can you conform the charger voltage output when plugged in to the wall socket ?