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Hi,

I have questions about keeping an older battery pack viable. My Miata was converted to EV in 2010 and batteries are somewhat creaky. (http://web.archive.org/web/20150215073842/http://www.kleenspeed.com/eiata/).

The car seems to have been parked outside and unused for some years but still runs, although with a range of approx 50 miles versus original claims of 80-90 miles.

The original batteries (36) are CALB LIFEPO4 200Ah (afaict) https://www.electriccarpartscompany.com/200Ah-CALB-SE-Batteries, so I decided to try replacing the weakest batteries in the system to keep it going a little longer ahead of a full battery refresh.

In any case, I replaced one battery (the one most with low voltage when under load, and prime culprit for low charge ahead of rest of pack). A couple of weeks later, I've gone back to check individual voltages per battery after full charge, and the new battery I added to the pack has a charge of 0 and resistance of 0. This decline was not reported by the battery monitoring system.

I suspect that the issue is that it doesn't match the draw characteristics of the rest of the pack, so has gone into a safety state, but wondering if it might just be a bad battery.

Any insights or suggestions would be much appreciated.

Thanks,
Michael
 

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Hi Michael

How did you ensure that your new battery was at the same state of charge as the others when you fitted it?

It sounds to me as it you have run it down to zero and the other cells have reversed it - killing it DEAD
 
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