It seems that Nissan has improved the 2018+ Leaf's ability to keep the 12 volt battery charged, but not by any means perfected it. I've mentioned before that I've seen my 2018's accessory battery at about 12.45 volts; well, we had my housemate's 2020 SV+ under a car cover for roughly three weeks, while the leaves fell. I fully charged the accessory battery before we covered it, but after uncovering it, said battery was at, IIRC, 12.17 volts. I was only able to have it on the maintainer for about 10 hours before she had to use it yesterday, so it will be interesting to see where it's at now, voltage-wise...
Scarlet Ember 2018 Leaf SL W/ Pro Pilot
2009 Vectrix VX-1 W/18 Leaf modules, & 3 EZIP E-bicycles.
BAFX OBDII Dongle
PLEASE don't PM me with Leaf questions. Just post in the topic that seems most appropriate.