Weird the Tesla main blog area states 1 to 2% a month if not plugged in.
In regards to the battery, Tesla you are right does have a deep cycle 12V battery, but originally with the Roadster it used the main battery and in 2010 according to this detailed blog changed to a 12V battery to keep things set for electronic settings. Very weird considering you could do it with the Lithium. Need to dig into this more to find out why as I am curious.
https://teslatap.com/articles/12-volt-battery-compendium/
Good info here on the Tesla's and the various 12V batteries each version uses along with a detailed image of where this battery is located.
Chevrolet Bolt when looking at the web site does not indicate any 12V battery, but I thought about it and dug up an owners manual and it does have a standard 12V battery for basic such as settings in the auto and access into the auto. Very weird as I would think they could use the auto main battery better for this. Page 22 of the owners manual states it does have a 12V battery in addition to the main power systems battery.
https://my.chevrolet.com/content/dam/gmownercenter/gmna/dynamic/manuals/2018/Chevrolet/Bolt/2018-chevrolet-bolt-ev-owners-manual.pdf
@Robert Hall I am sorry, I am wrong both Tesla and the Bolt have 12V lead acid batteries for basic settings in the auto info saving and access into the auto. if something happens to the high power system, you can still get into the auto via the 12V battery.
In regards to the discharge of the main high power battery pack, Chevrolet and Tesla official web sites are stating 1 to 2% reduction for just sitting. As @ykX has mentioned, looking around I do see Tesla owners who have posted up to 30% depletion upon sitting and it is clearly based on where one lives as the heavy drain seems to be common in cold weather areas.