Teslas are now old enough that there's large-scale long-term battery degradation data available. They lose roughly 1%-2% of capacity per year (that's a linear approximation, actual degradation is steeper in the early years, tapers off later). So after 15 years you'd expect 70%-85% of the range left.
Modern EVs have battery management systems that keep their temperature and other factors within the range that's gentle for the battery. EVs also have some spare "inaccessible" battery capacity that prevents them being (dis)charged to extremes that would shorten their life. 15-year-old EVs will be fine. EV batteries aren't your cellphone batteries.
Even my LEAF (which has one of the worst battery management systems in terms of having passive cooling only) is 7.5 years old and has around 85% of its original capacity.
I guess I don’t understand why that’s acceptable. 15% degradation takes you from what 350 miles from full to just shy of 300. How much worse is it in the winter? None of those things happen in ICE vehicles that are much cheaper than even the cheapest BEV.
ICE vehicles also lose range in the winter. Older EVs have resistive heaters but newer ones have heat pumps which use 1/3 the energy to produce the same heat.
It's way worse than that. Mine is a 2015, so has only a 24kWh battery. I'm down from around 90 miles to around 75 miles. Winter is less, but not catastrophically less.
When I was in an office, it was 8 miles away. Our grocery is 1 mile away. The farthest kids' friends house is 2.7 miles away.
As proof that there's utility there: the LEAF does more miles per year than our ICE car, so it gets plenty of use, even with the severely limited range compared to higher-end EVs.
As for why it's acceptable: the car was $22K new after incentives. In 7.5 years, I've just now changed the wiper blades and cabin air filter for the second time. I turn all the wrenches on our family cars and I have literally only put a wrench or socket to the LEAF once in that time: to remove and charge the battery after we parked it for almost 8 weeks when COVID first hit and my little OBD2 Bluetooth dongle ran it down. (Wipers and cabin air are changeable without tools, as is filling the washer fluid tank.)
If your regular commute is below 200-300 miles (I hope so!) it doesn't even affect your daily use at all.
I'm not saying it's great, but just want to highlight that EV batteries don't fail as quickly and catastrophically as you may expect from batteries in consumer electronics.
EVs aren't cheap yet, but overall cost of ownership can make sense. Other components of EV drive train are usually more reliable (fewer moving parts, not exposed to outside elements as much), and cost of fuel can be much cheaper. And switch to EVs is also motivated by factors that have indirect costs, like air quality and energy independence.
Modern EVs have battery management systems that keep their temperature and other factors within the range that's gentle for the battery. EVs also have some spare "inaccessible" battery capacity that prevents them being (dis)charged to extremes that would shorten their life. 15-year-old EVs will be fine. EV batteries aren't your cellphone batteries.