Battery repair help...replacement for damaged a123 26650 M1A cell?

[Bush mechanic]

Sad to say I have somehow damaged my old Em3ev (cell man) triangle battery pack whilst in storage. This was always a brilliant pack, bought about 10 years ago, 16s5p (52v nominal using 3.3v LiFePo a123 26650 M1A cells. It was used lightly for about 5 years before I charged it and left it in storage, but at some point it has either fallen or else been crushed causing one cell to split open.

It's an old pack so I can't justify spending too much time or money, but it probably has a bit of life left as a spare battery. My thoughts are to either

1) cut out the 5th cell on each remaining parallel group you make them all 4p (to rectify the imbalance and just make it a smaller battery, or

2) solder in a replacement cell. It won't be a hard job to solder in, soldering obviously not best practice but I've successfully done it before, but I would need a recommendation for a replacement cell to use...bearing in mind these are 10 year old 2300mAh 3.3v M1A cells which would by now have lost appreciable capacity! I can get hold of the newer a123 26650M1B cells but these are 2500mAh.

Could I ask if anyone with experience building and repairing packs could give some advice?

TIA!!

 

[MarcoWasRight]

Find a small pack of M1A’s on eBay or check BatteryHookup. I know Battery Clearing House has or had degraded M1A packs fairly cheap considering it was dozens of cells in a pack

Or make a post on a few forums asking if anyone would donate or sell some M1A’s. Specifically degraded ones. Best to try to test one group of your battery and divide by 5 to get a rough capacity. And also an IR measurement. I can’t imagine anyone would mind giving up an M1A. I have some M1B’s but I’m not at home and they are damn near 100% capacity and original IR so would probably cause an imbalance for you that a passive balancer would struggle with.

Keep in mind the can of the cell is aluminum so not only fragile but very hard to solder or spot weld. I would check all others for damage. Any that I dropped on my floor started leaking electrolyte. All 4 of them.

If you absolutely can’t find a replacement I’d happily send you two M1B’s. One to practice on and the other to install. Honestly not sure how I would get it to work in your pack. Would need 100’s of intense cycles. I could cycle it in my EBC tester but it would take days due to the 5A charge limit. I think cycling it at 8A charge and 40A discharge would be rough enough to possibly degrade it a bit in 100-300 cycles to get it down from 2.5Ah to 2Ah and maybe drive the AC IR from 6mR to 8-9mR at most

 

[Bush mechanic]

Find a small pack of M1A’s on eBay or check BatteryHookup. I know Battery Clearing House has or had degraded M1A packs fairly cheap considering it was dozens of cells in a pack

Or make a post on a few forums asking if anyone would donate or sell some M1A’s. Specifically degraded ones. Best to try to test one group of your battery and divide by 5 to get a rough capacity. And also an IR measurement. I can’t imagine anyone would mind giving up an M1A. I have some M1B’s but I’m not at home and they are damn near 100% capacity and original IR so would probably cause an imbalance for you that a passive balancer would struggle with.

Keep in mind the can of the cell is aluminum so not only fragile but very hard to solder or spot weld. I would check all others for damage. Any that I dropped on my floor started leaking electrolyte. All 4 of them.

If you absolutely can’t find a replacement I’d happily send you two M1B’s. One to practice on and the other to install. Honestly not sure how I would get it to work in your pack. Would need 100’s of intense cycles. I could cycle it in my EBC tester but it would take days due to the 5A charge limit. I think cycling it at 8A charge and 40A discharge would be rough enough to possibly degrade it a bit in 100-300 cycles to get it down from 2.5Ah to 2Ah and maybe drive the AC IR from 6mR to 8-9mR at most

Hey, thanks for the tips, yes I am thinking I will try to find a slightly degraded pack - thanks for the offer of the cells, I will keep that as a back up option - but I have also had another thought: I might try and find an old Dewalt 36v drill battery pack as they used the m1a cells I believe (really they were only 33v they used 3.3v 10s of course!)

I did try to experimentally solder the damaged cell, just to see how it would go...it is harder to get a good connection than I expected, but I did manage to solder it onto some scrap nickel strip.