We can clearly see a loss of capacity over time/use and definitely different numbers on vehicles with identical mileage. It's all expected. What is unexpected and encouraging is how the average shows that the loss degradation is slowing down and it seems to almost flatten out. In other words, everyone sees a loss of about 5% over the first 50k km and then only maybe 1% over the next 50k km.
I thought that was expected too, at least from some article i read. 3-5% for the first 50k miles. Then 1-2% every 30k miles
thank you for the quick replies. I see the chart is done by distance, and wonder if its really age that is more of a factor. Either way, I agree, the battery ages similar to what we see in our cell phones that there is a quick fall off, then plateaus, as the chemistry of the batteries stabilize.
Well, I have three years and more km than your chart shows. I have 7% loss. I charge at 30 amps, rarely supercharge, never to full. I think that it is mainly heat and time, not miles. This chart does not tell us what causes degradation. But it nicely shows degradation tapers off after a few years.
Interestingly, Tesla has been keeping data from the first. They don't share much, but THEY say it's time, not mileage. You notice their drive train warranty states "Eight years, UNLIMITED miles".
But what do they know, right?
Degradation comes from both use (charge-discharge cycles) and from ageing. These effects are not additive. Rather, in most cases use should be the main driver of degradation. Time spent at very high or low state of charge, depth of discharge cycles, temperature and overall useage are the most important factors here. If a battery is in little use however, pure ageing will be the main driver of degradation.
A slightly different question about degradation: let's say you drive just 10 or 20 miles a day and recharge each night. Is a long history of shallow discharge cycles like that bad for the battery's health? Or should you more deeply discharge cycle the battery periodically?
I assume from the statement above that the answer is "no" ?
I don't believe the theory time being the main factor over use. I have 60k miles yet cars with the same mileage that are much older than mine have the same degradation. So if time was the more important factor it would certainly show more impact.