Mechanics have been doing that for about 100 years now. It’s not complicated to judge the “health” of an engine. Compression ratio, exhaust composition, even just the sound of it to a trained ear.
While the cost of replacing a battery in an EV is high, it’s not very different than an engine and transmission.
While the cost of replacing a battery in an EV is high, it’s not very different than an engine and transmission.