I was under the impression most EVs cut off the connection to the high voltage battery almost all the time they’re not in use.
They rely on a 12 V battery or a 48 V battery like a normal car.
The only thing I’m aware of that special is that if that low voltage battery gets low enough the car will detect it and recharge it from the high voltage battery, temporarily connecting it for that purpose.
Which leads to "fun" situations when that battery runs out, like not being able to get into your car or start it. However not much power is needed, so a tiny portable jump pack is enough to get things going.
Both me and my sister has experienced this, me a Nissan Leaf and her a VW ID.4, good times.
The latter can be an issue as my sister got stranded in the mountains during winter. Battery ran flat while they were on a long ski trip, and they couldn't get it fired up when they got back. Took a few hours before rescue vehicle arrived and gave them a boost.
That really enables them to have a continuous state of power supply for a long long time. This cannot be achieved by ICE cars and not even hybrids for that matter.
This puts a cap on how much the "smart" systems can do because it dramatically increases cycle count and thus the risk of the 12v battery losing the ability to produce enough voltage to start the car, leaving the driver marooned somewhere.
It could also result in a noticeable "vampire" drain on the high voltage battery which looks bad and could put you at a disadvantage vs. competitors.
So extra drain would be an extra big problem.