[lutorm]

At least on our PHEV, when you read out the battery module state with an OBDII reader, you get to know not only the current estimated capacity but also how much time it's spent at various states of charge, how much time it's spent being charged and discharged at different currents, how much time it's spent at different temperatures, and a completely absurd amount of other diagnostics.

I'd feel a lot better about the state of the battery if I bought one used, rather than the state of the ICE. It's possible to borescope it, but you have no way of telling how long the previous owner went between oil changes, if they flogged it out to redline regularly, etc.