@internalaudit
to know li-ion hold, look at the most largest scale real world test: electronic devices, namely smartphones. battery is unusable after three years and should be replaced, just in time that new OS is not updated/supported.
To be fair, many of the 1st gen Nissan Leaf batteries are still functioning after eight years but likely a good proportion of those at a reduced capacity. But we have to remember the eight year battery was dictated by US and other government so it's not through the automakers' largess that the batteries are covered eight years.
The Tesla Model S batteries may be holding up better with liquid cooling and good thermal management system.
There's the reserve/buffer capacity that Tesla slowly releases. That is most likely why people are thinking their batteries are degrading by 1% each year. They are extrapolating that to mean their batteries will last at least 20 years, or maybe some even think they will last 100 years.
With constant charging, occasional fast charging, hot climate, occasional depletion to below 20%, calendar degradation, rapid acceleration (some of which Toyota bZ4X and Lexus RZ are trying to avoid), freezing temperature charging, all these variables are going to cause many battery cells to eventually fail before the 1,000 full charge cycle. It's law of average so some will last longer and many will last the average but some cells will die sooner.
Problem is it doesn't seem to take a whole lot of failed battery cells to cause issues and the medium to long-term solution is not to replace bad cells with good cells as per my reading on Tesla Motor Club. There's more to it than that and there will be various scenarios requiring their own individual solutions.
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