The cells being used could most definitely be a factor the wtt ones found in some models torn down earlier in the thread are dubious at best, even the Chinese call the company untrustworthy. The capacity decline has been noted in other situations not just under car bonnets some batteries have burnt though the housing being stored in a warehouse without a single cycle.Regarding the DCS batteries which are presumably the focus of this thread, my wonder is if it is the heat of being located under the hood of the vehicle which is causing the capacity loss. If so, even an indoors battery here in the tropics may suffer the same, or similar, fate.
It would be nice to know the actual cause of the capacity decline, for then methods to mitigate the problem might be considered. My personal opinion based on what I have seen so far is that it is not the quality of the company's batteries that is the problem--it's their stubborn insistence on inflated performance hopes--hopes which simply cannot be met in the real world. It appears they simply need more rigorous testing of their own equipment, and a humbler, more honest, advertising based on the results.
Obviously the excessive heat of being used under bonnets will be a factor but I think the reason those cases have been more prevalent because that's the primary use the batteries have been sold for.
I still can't believe Toshiba built the BMS as I'm 95% sure Toshiba would use components they manufacture themselves in a product apparently made by them.
The whole thing stinks of lies, half truths and poor quality components to me but time shall tell.