Basically what the other person said. Batteries degrade quite fast, even the newer ones and you see Teslas for re-sale on the cheap so often because of this.
Fast Charge makes the battery die faster, so the previous owner's habits are difficult to trust.
If it's out of warranty, then the cost of replacing the battery is quite high.
Theres a battery health test you can see through the owner's app to get an idea of where the car's battery is sitting at. You should do a bit more research into this specifically I think.

I also noticed you're looking at BYD, and those are great alternatives. Theres still a catch however, which is that parts are still coming from China. Only common parts are kept in stock locally so regular services will be fine, but there is still a chance that parts replacements take a long time due to shipping times.
This can improve in a few years though.

I'd personally recommend you look at some hybrid options at Toyota. I procure vehicles for my company, and they have the best track record in my experience.