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Is it possible to harm the battery post 90%?

1687 Views 5 Replies 4 Participants Last post by  TimBolt
Hi Forum Members,

I have searched on this forum and on the internet, but have not yet found the following question answered:

Will the battery on the car be adversely affected if a charger is left plugged even after the car has reached "full" with the Hilltop Reserve setting on? I am predominately interested in knowing if the battery conditioning and longevity will be impacted if, say, I charge my car from 50% to 90%, but then leave it there to run errands for another 1-2 hours. During that last 1-2 hours, is there any harm done?

I use ChargePoint.

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Based on postings on this site and further readings on other sites, the common wisdom is to not charge to 100% every time, but to turn on hilltop reserve (which stops the charging at about 87%) in order to maintain the longevity of the battery pack. So, no direct harm, just reduced battery life.

Interestingly, my old 2013 Volt prevented ever fully charging the battery (even though the battery gauge would read full), towards preserving the battery in the long term. I originally thought this was the case with the Bolt as well but it appears not.
The Bolt does have unused battery capacity, limited by the charging software. A 100% charge does not use 100% of the battery’s actual capacity. There is no definitive answer as to how much “headroom” GM has designed into the battery management software, most estimates I’ve seen are in the 5% to 10% range.
Thanks for that! Now I know why on the Bolt battery pack itself it indicates 57kWh: because the difference between that and the true capacity (60 kWh) is 5% (3 kWh) of the total capacity, or what is held back! ?
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