With the wider release of the 2019.24.4 firmware update, Tesla seems to have changed how leaving your car plugged in behaves.
In my very limited 2 days of observation so far, the new 2019.24.4 behavior keeps the car at your desired charge limit even hours after charging completes. To achieve this, more functions seem to run off wall power, one such being the cabin overheat protection.
Checking my Sense energy monitor, my nightly charge completed at 4:30AM. At 6AM, a 2-3 minute 8kW load topped the battery back up to 90%. Then, at 10:19AM, the car started to pull power from the outlet. Usage bounced between 300 and 700 watts. About 10:15AM is when I grabbed my phone, which triggered Tezlab to wake up the Model 3. Once the Model 3 is out of deep sleep, cabin overheat protection is able to kick in. Going outside I could hear the AC on and see the TESLA letters on the mobile charger pushing electricity into the car.
Once I opened the door and unplugged the car, power usage stopped immediately. Plugging the car back in, it took 15 minutes for this cycle to repeat itself. It seems as of 2019.24.4, this is a new feature Tesla has implemented. I’ve gone back and checked previous hot days when the car was left plugged in. The Model 3 never pulled from the wall unless I turned on the air conditioning from the app.
While it is nice for the car to try and leave as much power in the pack as possible, using that much electricity all day could be less than ideal. If you rely on Time of Use rates at night, this kind of defeats the purpose. Hopefully Tesla makes this behavior something you can disable. Either that or users will have to disable cabin overheat protection, letting their interiors cook, or unplug their car after the charging session has completed.