Charging to 80% capacity

[alohart]

While battery chemistry itself is to some degree responsible, power density tends to be the more significant factor. I.e., because the 60Ah cars must use 2x the capacity of the cells in the car vs a 120Ah one, they are essentially getting cycled twice as often - which is a major driver of decay.

Our new 2014 60 Ah BEV lost ~25% of its usable capacity after having been driven only 13k miles over 7 years. Our used 2019 120 Ah BEV had lost <5% of its usable capacity after having been driven 32k miles over 3 years. Our 60 Ah battery pack had experienced fewer charge-discharge cycles and more aging than our 120 Ah battery pack. So in my very limited experience, age was a much more important predictor of degradation than the number of charge-discharge cycles. However, there are way too many factors and way too few examples to draw any general conclusions from my experience.

There is one oddity about our 2014 BEV that I've always wondered about its relevance: it was stored every year for a total of 3 years out of our 7 years of ownership. I always stored it at a charge level between 40% and 60% and at an average temperature of ~77 ºF (25 ºC). I've never been able to find any suggestion that a battery cell that isn't being charged or discharged regularly degrades more rapidly. However, maybe this is true.

 

[Gonville]

Our new 2014 60 Ah BEV lost ~25% of its usable capacity after having been driven only 13k miles over 7 years. Our used 2019 120 Ah BEV had lost <5% of its usable capacity after having been driven 32k miles over 3 years. Our 60 Ah battery pack had experienced fewer charge-discharge cycles and more aging than our 120 Ah battery pack. So in my very limited experience, age was a much more important predictor of degradation than the number of charge-discharge cycles. However, there are way too many factors and way too few examples to draw any general conclusions from my experience.

There is one oddity about our 2014 BEV that I've always wondered about its relevance: it was stored every year for a total of 3 years out of our 7 years of ownership. I always stored it at a charge level between 40% and 60% and at an average temperature of ~77 ºF (25 ºC). I've never been able to find any suggestion that a battery cell that isn't being charged or discharged regularly degrades more rapidly. However, maybe this is true.

What level was it charged too? The 2014 60Ah? The manual always used to say store it fully charged? Pretty sure cell balancing would have been significant factor over that length of time. Still as seen 7 years at 2% a year should have been around 14%.

 

[Dutchi3]

Still as seen 7 years at 2% a year should have been around 14%

I can confirm this. I lost about 20% in 10 years. Still able to do 75-80 miles with a velvet right foot and in moderate weather.