that's not how car batteries work. phone batteries suck because they are incredibly space and weight constrained and they're too small to effectively include thermal management. Toyota warrentees their hybrid vehicle batteries for 10 years/150k miles for 30% range degredation. after that, since it's a relatively small battery some looking around suggests that the cost of an out of warrentee replacement is roughly $4000, and needing the replacement is relatively rare over the life of the vehicle
Not only is Toyota's warranty on Prius batteries quite good, a good chunk of the battery issues with older Priuses come down to corroded terminals. A dealership will happily throw a new battery in there for a few grand, but a good indie hybrid mechanic knows to try the cheap and easy fix of cleaning the terminals before replacing the battery (and will recommend reconditioned battery packs for a serious $$ savings)
