That's a (mostly early model year) Tesla problem, not an electric car problem. My Nissan LEAF sat unused in my driveway for several months in 2020 and its charge level didn't drop at all.

I would think the ambient outdoor temperature would have a rather large impact here. If it's cold outside the car has to use battery power to keep the batteries themselves within operating range.

The Nissan LEAF's battery warmer only activates at -17C and turns off at -10C.

It does not reach -17C any day of the year in much of the world.

First I'd have to find them, but I've never heard of that happening. On the other hand, I've had plenty of battery problems in ICE cars.

I bought a bunch of LFP cells a couple years ago to do an EV conversion of a Mazda RX-8. After a couple years of literally just sitting there, they went from about 3.2 volts to about 3.1 volts.

Tesla cell chemistry is different (unless you get one of the new ones that use LFPs from CATL), but it's not an inherent problem with electric cars generally.

Late to reading this comment. That's a beautiful option for an EV conversion, how's it going / how'd it turn out? Is there a progressive diary blog or somesuch?