Battery capacity loss after sitting idle for a few months

[Davidmnz]

I think my battery is dying. I bought the 36V10AH bottle battery (and motor) in March and rode for a few months with no problems. Then I didn't ride for about four months. During this idle time the battery was left fully charged in my lounge. The battery has never been subjected to high or low temperature extremes. I did hit the low voltage cutoff at the end of one ride but the battery capacity was fine after recharging.

Now the battery seems to have much less capacity. Today I hit the LVC less than 1 km from home. I had rigged up a voltmeter connected to the charging port so I could see that the battery voltage dropped rapidly to ~32 V with any sort of load. The no load voltage was 41.4 V at the start of the ride but dropped rapidly to 36 V or less.

I have charged the battery twice since I resumed riding a couple of weeks ago and it has charged up to ~41.5 V both times.

Am I right in thinking I have a dying or dead cell or cells? What is the GM battery warranty period? Any suggestions for further diagnoses?

[Andrew]

I think you have determined the problem, leaving it fully charged for a long period will definitely make it lose capacity. It would be hard to determine if individual cells are to blame unless you took apart the pack and did some proper discharging experiments on each one which would not be straight forward