Stripping a battery to test it

[Scorpio]

Hi folks,
I have a couple of 36v batteries which are not performing well.
I’ve seen a few threads on testing each cell group to see if it’s one cell or group that’s the problem. I’m happy stripping the battery and testing it.

My question is how do I re-wrap it if / when I’ve fixed the problem?

Battery 1 is 36v 10ah fish style, history unknown but it’s on an older beach cruiser bike, hits lvc under load in about a mile.

Battery 2 is 36v 12ah rack battery, bought new about 3 years ago and never used (but may have been abused / mishandled by the installation “specialist” !) it is flat by the time it completes a 5 mile test route.
I’ll post voltage readings later..,



Suggestions (or links to battery test / rejuvenation threads) welcome !

 

[Andy-Mat]

Hi folks,
I have a couple of 36v batteries which are not performing well.
I’ve seen a few threads on testing each cell group to see if it’s one cell or group that’s the problem. I’m happy stripping the battery and testing it.

My question is how do I re-wrap it if / when I’ve fixed the problem?

Battery 1 is 36v 10ah fish style, history unknown but it’s on an older beach cruiser bike, hits lvc under load in about a mile.

Battery 2 is 36v 12ah rack battery, bought new about 3 years ago and never used (but may have been abused / mishandled by the installation “specialist” !) it is flat by the time it completes a 5 mile test route.
I’ll post voltage readings later..,

View attachment 46077

Suggestions (or links to battery test / rejuvenation threads) welcome !

Good question but with some possibly unfortunate answers for you, here are a few pertinent points for you.
If you are inquiring to see if you can repair/replace some cells, you will be just throwing your money away. All cells have to be identical, and I mean identical, and all replaced at the same time.
Any old cells still working might be repurposed for Flashlights and other things (Vaping???? )l! But you will need a simple charger to charge cells individually, around 10 UK Pounds on ebay.
A battery, for reliable operation, needs to be (re-)built by cells from a good manufacturer. Ones of the exact same type. Tested to be within certain tight parameters - matched is the correct terminology I believe, and hopefully made on the same day.
Though I personally believe that all of the cells in both of your present batteries are now going defective, and there is nothing that can be done, and you will not want to "match" them.
There are some good videos on YouTube, and some great websites, that show you how to correctly replace all the cells in a battery at one time.
My personal tip is NOT to buy from resellers, buy them as a matched set from the company that made them.
The battery made from such matched cells, and carefully used and treated, will last far, far longer.
There are (sadly) many different opinions on Pedelec about batteries, you will need to try and sort out the wheat from the chaff when reading.....
Your first two batteries, did not IMHOO last as long as they could have with proper maintenance and usage (assuming reasonable quality). I myself have given away good working Lithium batteries that were 8 years old and intensively used, which were Panasonic cells, and went on to be used further by the recipient of that old bike....
Only slight loss in range was apparent to me, but I did not measure it in any way, shape or form. More of a feeling to be honest!
My latest e-bike also has Panasonic cells in both batteries, and are both still in good working order at almost 5 years old!!
If you wish, I can make a "does and don'ts" list, but only if you wish, as many here simply do not believe such things, and rapidly get rude and obnoxious if anyone disagrees with them....!
regards and best wishes.
Andy
PS. Thee are some good battery re-builders around, and I am sure that other members here can recommend a company for such work for you. It should save you some money as well over a new battery.

 

[Nealh]

Two options Scorpio, carefully cut the wrap along it's length. Then reuse it and use tape to hold it together again or buy some new heat shrink wrap sleeve and use a hairdryer to shrink it.
If buying wrap measure the two different side/widths of the battery and add them up, then add 25/30% to the measurement and this is the flat size wrap to buy.
Eg; side a 75mm + side b 105mm = 180mm add 30% = 234mm so buy this size wrap or a near size in flat form. Don't try and work out the diameter size, the flat size route is far easier.
Heat Shrink Tube Tubing Wrap Sleeve Blue 240mm x ½ metre 18650 Battery UK Stocks | eBay
I usually order from AliExp and keep some extra for future use.

What voltage readings do the batteries give after a full charge ?

 

[Scorpio]

@Andy-Mat i didn’t explain it too well, I’m not planning to replace any cells, I’d like to check if all groups are failing it if there’s one group out of balance - that I can maybe charge directly so it’s nearer balanced.

@Nealh many thanks as always.

After full charge and resting for an hour :
Fish battery is 40.5v
Rack battery is 40.3v
Odd as the rack battery fella feels stronger ...



I’ll be going for a few short test rides to see if they improve with a bit of use. Both or on fun bikes to lend out when mates visit so poor is ok but these are TOO poor. Thanks for the help !

 

[Nealh]

Both of those voltages indicate a problem but one won't know until cell group readings are checked. It might just be an imbalance on a couple, if one had a real duffer cell group the BMS wouldn't allow charging if one fell below 2.8 - 3v.
If one had a dead cell or a very bad cell then one wouldn't know without deconstructing the whole group or could see signs of leakage or damage.

 

[Andy-Mat]

@Andy-Mat i didn’t explain it too well, I’m not planning to replace any cells, I’d like to check if all groups are failing it if there’s one group out of balance - that I can maybe charge directly so it’s nearer balanced.

@Nealh many thanks as always.

After full charge and resting for an hour :
Fish battery is 40.5v
Rack battery is 40.3v
Odd as the rack battery fella stronger ...

View attachment 46078

I’ll be going for a few short test rides to see if they improve with a bit of use. Both or on fun bikes to lend out when mates visit so poor is ok but these are TOO poor. Thanks for the help !

The BMS is supposed to do just that....keep the groups in balance, usually by bleeding off some power from the cels that charge to a higher voltage.
That is why they are built into e-bike batteries. But some do waste some energy, due to the design/method used....
The voltages fully charged you are measuring are low, (assuming an accurate meter and a 36 volt nominal battery), it should be much closer to 42.00 volts if the cells are good, and the charger is good of course!
Even after many months of not being used or charged, a good quality 36 volt battery will show at least 40 + volts, in my experience.
Directly after the charge, very close to 42 volts! Check charger output.
Of course, a possibility is that the BMS is failing, though I myself any of my biking friends that I know of, have had such a failure, though I do believe there was a post here on Pedelec about such a problem.
The most likely is simply the battery is aging rapidly, and a "re-cell" is needed....
It should be easy to test once the battery is opened and you do some simple measurements with a reasonable volt/multi- meter.
Let us know what you find out.
regards and best wishes
Andy

 

[Scorpio]

Thanks gents,

I've opened up the Fish battery, I get readings for 10 cell groups, all voltages are similar and in range 4.04 - 4.05 giving total 40.5

Fish bms :


I have 2 chargers here (1 known good from my bike, 1 that came with the 2 "problem" batteries), will try a few more charge cycles and compare the chargers, then post up the results.

 

[matthewslack]

Thanks gents,

I've opened up the Fish battery, I get readings for 10 cell groups, all voltages are similar and in range 4.04 - 4.05 giving total 40.5

Fish bms :
View attachment 46081

I have 2 chargers here (1 known good from my bike, 1 that came with the 2 "problem" batteries), will try a few more charge cycles and compare the chargers, then post up the results.

40V is fairly high up the charge curve, so you should have maybe 70% or a bit more of the capacity available. If you get very little useful range from 40V then probably cells are the issue.

Worth charging and measuring full charge V with the charger connected to verify if it gets to 42V. If it does, then drops off to 40V, again, cells suspect. If it doesn't, charger suspect.

 

[Nealh]

All cell groups are balanced to .01v so pretty damn good , if they don't charge to 4.15v - 4.2v then one has to think that the capacity has somewhat reduced and time to recycle them. Likely internal resistance will be high and they will sag a lot, one could deconstruct them for torch cells.