How does the Tesla battery warranty work?
I wish I knew.
With the exception of one specific case, the Tesla battery warranty doesn't appear to be worth the paper it's written on. At least not at first glance.
The specific case is fire. If the battery catches fire for any reason except deliberate tampering, or the car was written off before the fire, you will get a replacement car. Rumor has it that in the single case of a battery fire that has happened after this warranty was introduced, the owner got a pretty sweet deal.
Quite a few people had their batteries replaced under warranty, mainly due to two causes, none of which have anything to do with the things we care about in the battery (and who knows if they're covered by the battery warranty, or the general one):
- Early cars had poor quality contactors in the batteries, which tended to "pop" at inopportune moments (and made a really cool squealing noise under acceleration). Initially the whole battery was replaced when this happened. The recall was in early 2015, and didn't involve replacing the battery, just the contactors. Strangely it attracted zero press. Well done Tesla. :)
- Coolant leaks. There's lots of piping inside the battery to carry coolant. I've seen a number of cases where these have sprung leaks. This tends to lead to a battery replacement, but you get a refurbished battery, and the repaced battery is itself refurbished.
Tesla has (wisely IMHO) refused to specify any kind of minimum capacity expected from the battery in 8 years, and so you really have nothing to measure the warranty against. It just states that "expected" battery degradation isn't covered. Duh.
When you look at battery degradation in the Model S fleet so far, I'm not worried: