My Battery appears to be Knackered - Advice sought.

[jackhandy]

Afternoon All,

The "Bottle" style battery on my missus' Powabyke X6 (36v) was fine last weekend, but is now showing 23 volts on a multimeter & 2.3 volts when a wattmeter is plugged in:
When I stripped the battery housing, I found about 1/2 cc of water in the bottom & some rusty discolouration on the connectors of the bottom cells.


There doesn't seem to be any kind of BMS:

Having left the pack in the airing cupboard for 48 hours to ensure drieth, if I connect to the charger, the charger light remains green (indicating it's not charging).



The cells are marked Sanyo:

Is there any possibility of salvaging the entire pack & recharging it?
Or am I better-off biting the bullet & buying a 36v battery which has a BMS?
Is it likely I could salvage any of the cells?
Is attempting to recharge it likely to damage the charger?

 

[oigoi]

If you could figure out how the cells are connected together (probably a mixture of series and parallel you coul maybe use a voltmeter to track down which cells are still ok and which are dead. I have done this in the past to make one good battery for a laptop out of two duff ones

 

[Deleted member 4366]

It looks like 30 cells from your photo, which would mean 10S3P or 10 in a line and 3 wide. What's probably happened is that one or more groups of three have gone down below the minimum voltage and need to be persuaded back up to a level that the BMS can handle. You need a voltmeter. Hopefully you can get at the balance wires that run to the BMS, where it would be easiest to check the voltage of each group of three by measuring between each pair of balance wires.Once you've identified the offending group/s, you need to charge them up with a single cell charger, but best done sooner than later. You can do it with a 5v USB charger or if you have any charger that does 3.7 or 4.2v lithium batteries as long as you monitor the voltage until they get up to the same as the others. Don't leave it on 5v and forget about it.

 

[Scimitar]

Is it likely I could salvage any of the cells?
Is attempting to recharge it likely to damage the charger?

They are 1500mAh cells, according to this...
https://master-instruments.com.au/products/59045/UR18650W2.html
Check them out with a DVM and see if any have fallen below 2.5V - if you find any that have, bin them, they will become dangerous. Above that voltage, slow and careful charge of about 100mA and get them up to at least 3.5V, then you can whack them into a normal lithium charger with a properly regulated cut-off at 4.2V max. Beware, some of the cheapy nasty chargers don't actually properly cut off and continue to over-charge, which makes them become dangerous cells again.

 

[jackhandy]

Thanks for the advice - It seems a bit of a ropey setup, with 3 parallel- connected stacks of 10 series-connected cells in each:
No bms or balance wires.

I've ended up with 19 cells reading ~ 2.7 volts & 11 reading from 0.0 - 1.5 volts, which is a bit of a bummer, as 20 gooduns would have been handy.

The data sheet that scimitar linked to shows that I had one of the 4.5 ah batteries that Powabyke labelled as 6.0 ah, so that's one question answered.

Thinking of replacing it with a Frog 10 ah: BMS & Greenbikekit have them at sensible prices, but will possibly screw me on delivery charge, as it's a battery.
36V 10A The frog type battery for electric bikes/36V 10Ah Battery Pack for electric bike with charger-in Electric Bicycle Battery from Sports & Entertainment on Aliexpress.com look promising, but has anyone dealt with them? I'd apreciate advice from those with more experience of dealing with Chinese suppliers.

If anyone has a better solution, please speak up.

 

[Deleted member 4366]

What about this one? About £200 including shipping and duty.
bottle ebike battery

 

[Jeremy]

It seems a bit of a ropey setup, with 3 parallel- connected stacks of 10 series-connected cells in each:
No bms or balance wires.

It's not a great set up, and owes more to the ready availability of very cheap laptop cells than anything else. These 18650 size cells are extremely cheap in the Far East, so it's been very tempting for ebike battery pack suppliers to use them.

The main problems with them are:

1. These cells have a pretty high internal resistance, so aren't suited to even a modestly high rate of discharge. They are designed to discharge at around 0.2 to 0.3C in a laptop, yet probably get asked to deliver peaks of around 2C on an ebike and an average of maybe 0.8 to 1C.

2. Because these packs have to use large numbers of cells to get the capacity and discharge rate to an acceptable level for an ebike battery they can suffer from mechanical and electrical problems with the inter-cell connections.

3. Quite often the smaller packs don't use a proper BMS, so there is a grave risk of cell failure. Not using a BMS doesn't present a massive safety risk with these particular cells, as their high internal resistance means that they are unlikely to be able to pass enough current under fault conditions to blow.

Some bottle packs are reasonably OK, and use a small BMS up in the lid. They all suffer from the high internal resistance cell problem though, a problem that is guaranteed to reduce performance and shorten life. Even the very best 18650 cells available have an internal resistance that is significantly greater than most other ebike cells; they are actually designed like this, as a safety feature when used in laptops etc.

 

[jackhandy]

Hopefully, the current replacement powabyke battery is of better design (and actually 6ah):

It should be, for the asking price of £300!

However, I'll be shopping for something a tad more robust.

 

[jackhandy]

What about this one? About £200 including shipping and duty.
bottle ebike battery

Hi d8veh, I considered that one, but it's going on the bouncer & the only places it would fit are under the diagonal, which is where the old battery was & picked up wetness (presumably from the front wheel), or on top of the crossbar, which potentially puts it in severe contact with my cruet



In your opinion, does this one represent a good alternative? It has a decent continuous output for about £8.00 more.

36V10Ah Li-Ion "Little Frog" EBike Battery Pack - BMSBATTERY