Good point. The beauty of a scientific paper is that they supply references that you can look up (there are 17 in this paper). These references will justify their methodology and experimental approach. Also, you have to consider what the experiment was trying to assess. This one was the effect of regenerative braking on battery degredation. The calendar degredation was not their primary goal, mearly a baseline to measure against.I'd like to see at least one other independent study which corroborates the finding in this paper that age related degradation is slightly less at 100% charge than 80%. Can anyone find any unrelated research drawing the same conclusion ? Otherwise it could be a case of picking one piece of evidence that happens to agree with a certain view point.
I've read quite a few battery research papers and also manufacturers cell datasheets over the last few years of EV ownership and this is literally the first one I've seen that came to this conclusion. Also, you have to wonder why a company like Tesla would make 80% charge the default and strongly recommend only to charge to 100% for long trips if it was actually less harmful to charge to 100%.
Because no other research that I've seen agrees with the claim in this paper I have to consider the possibility that there is an error in their methodology.