Always check if that suspiciously cheap second hand EV you're buying had active battery cooling.

A lot of the crap like the early Nissan Leafs didn't. And between that and the first gen EV battery pack design being shit in general, the battery pack just cooks itself. Its capacity falls off a cliff over time. This is where a lot of those early concerns about EV battery packs being hideously expensive consumables was coming from.

If the battery pack is actively cooled, then, as a rule, it ages gracefully. If not? Oh boy.

This is not a general rule and many non-cooled and air-cooled batteries can hold up pretty well. The battery cooling becomes a limiting factor for DC charging, especially if multiple charging sessions are required per trip.

The Leaf limited battery life is mainly to its battery chemistry (LMO), although it arguably doesn't go to great lengths to ensure thermal stability of the pack.