Wally (Forum Supporter) said:
How often are batteries going bad? We have a few very old hybrids in my office, first gen Escapes, original Camry and Highlander hybrids. all well over 100,000 miles and poorly maintained. One out of nine has been in the shop for a battery issue. They've been a very small percentage of repairs on our hybrid buses over the last 15 years, and in four years we've been running them our electric buses haven't had battery issues. The same can't be said of the engines, transmissions, and especially emissions systems of our diesels.
I'm really going to rephrase things from this page from Battery University. PRODUCE THE CHART
What the berk is this. Basically, lithium-ion cells are ranked/rated by "cycle life", which is a single full drain then recharge- typically 4.2 volts to 2.8. A common consumer grade cell for something like a vape pen (which frequently see that constant heavy use) have a lifespan of about 1200-ish, maybe 2000 full draws. If you consider a single cell to be your "entire battery" for the purpose of this discussion, that's a full "tank" being expended then recharged about 2,000 times.
Except that's a common consumer cell that yeeted into a cancer stick, not an OEM grade part for a car with a warranty. All EVs NEVER charge to "true" full- the absolute max a Tesla will charge individual cells is about 4-4.1 Volts each, both for longevity AND for safety. If you look at the website that promptly doubles your uses from 1 to 2,000 alone; but Teslas also tell you, to charge even LESS than their "100%" for longevity AND to charge slower at home for the same reason. Finally, you're rarely ever doing a constant depletion, you're using 20-30% on days just dicking around doing your usual.
What does all that E36 M3 mean? If every day you spent 30% of your lithium batteries power doing stuff- day in, day out- and never brought it to full, you'd have a functional battery for over 6,000+ days, or over 16 years. Of course this doesn't get into temperature controls or use cases, but many hybrids are never fully using the battery at any point and thus, have nickel-metal cells in priuses lasting 15-20 years with no issue. Considering that a full-cycle on the smallest tesla battery anymore is over 250+ miles of driving, you'd have to be a very specific group of people who would ever potentially burn one out from constant drain alone.
EDIT: This also doesn't get into wether the battery is specifically designed for longevity or not, AND only for lithium-ion. For Lithium Iron Phosphates, you'd double the lifespan.