My assumptions are fully baked.
So you're saying a car doing nothing will be 10x more efficient with a lead-acid battery vs a li-ion? I don't know how you came-up with your assumptions, but they seem half-baked at best.
The lead-acid battery has an larger initial energy reservior. Other than that, energy consumption should be very similar.
This 12V LFP battery is designed/created by CATL and works at low temps.
If the current 12V lead-acid battery, with a rating of 45Ah, can power the Tesla Model Y's essential 12V systems for ~24 hour before needed to be recharged from the Tesla vehicle's main battery pack then a battery with ~7Ah capacity will need to be charged more frequently due to the lower capacity.
The current 12V lead-acid battery will charge approximately once every 24 hours for ~2 hours. The anticipated 12V lithium replacement battery, with only 1/6th the capacity, will need to be charged more often. I estimate the 12V lithium battery will need to be charged every 4 hours for 30 minutes.
Any time the Tesla Model Y vehicle is awake it is consuming 230W just because it is powered on. Adding some power used to charge the 12V lithium battery (estimated at 15V and 10A (150W)) the total power drain during each charging period will be ~380W. Do this 6 times a day for 30 minutes each time and this would consume 1.14kWh per day, 7.9kWh per week.
By comparison, if the current 12V lead-acid battery charges for 2 hours every 24 hours this would consume 380W X 2hrs = 720Wh, (37% less power) per day. (I know that, recently, when I left my 2020 LRMY parked, unlocked for a week that the battery only lost 1% of the charge. Maybe the Tesla Model Y enters a deep sleep mode when parked for an extended period where is consumes less power.