Posts: 84
Joined: Tue Nov 14, 2017 3:47 pm
Location: GTA, Canada

Is my battery slowly dying?

Sat Dec 29, 2018 9:54 pm

Had a strange thing happen to me a few days ago.

Left my house with a full charge to go to the mall 5km away. Normally I charge to 80% but some plans changed at the last minute.

It's cold and I was running the heater so I arrived with about 82%.

When I came back to the car about half an hour later when I started the car the SoC indicator started out blank and I slowly saw the bars appear. I've seen this behavior with a dead 12V battery but mine is only a few months old. When I finished I had one bar less than before(13, I had 24 when I parked). I checked OVMS and it now showed 72% SoC. I checked the BMS and cell #76 was way lower than the others. The others were much closer. I drove home and lost about 20km on the RR on a 5km drive.

I charged it back up to 80% and it seems fine now. I did a risky 100+km trip in the cold today and made it back with 2 DC charge sessions. I watched the BMS constantly but the cells were relatively level, and #76 was no different than the others.

I'm doing a full charge from 20% now to run the cell balancing, it's been about a week since I ran it last.

Is one of my battery cells dying or is it just a fluke. My 2012 has about 48,000 kms now.
2012 i-MIEV SE Premium

Posts: 14
Joined: Tue Apr 19, 2016 5:53 pm

Re: Is my battery slowly dying?

Sat Dec 29, 2018 10:39 pm

If the battery is dying, the problematic cell will no longer be able to balance and it will always stay lower.
On my 2012 i-Miev, the bad cell degraded quickly within 5 weeks before the entire pack was replaced under the warranty.
week 2:
week 5:

When its cold, I also sometime see the battery level starting empty and slowly going up.

If a cell goes bad, when you do a full charge, the energy meter will not reach 16 bars.

To my knowledge, the battery only do a balancing session if you charge from 2 to 16 bars.

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