Your hypothesis about how the FIt EV charged and PCs sounds reasonable. It would be as if at the end of charging when the charging tapers down there isn’t enough power to fully handle the rather high demand of the PC. So then it pulls from the battery. Poor design. I’m not having this problem with my Charge Point Home level 2 EVSE. When topping off a charge for a long trip, I started PCing when the taper was at a very low point (first small peak, then large PC peak), then the power spikes for the ~30 min of PCing. I left with full bars and 100% SOC on HL. Range was normal. I have also PCed after charging is over and likewise left with a full SOC and normal range. So it’s apparent that preconditioning uses well over a kWh with temps in the 30s F, and if it’s not coming from the EVSE, you battery’s SOC (and range) are going to take a big hit. I don’t know why yours is acting the way you describe. Notes: The time scales of the two graphs are very different. The first is just 30 min while the second is 7 hours. In both, the preconditioning used about 1.3 kWh. This was with temps in the 30s F. I expect bigger draws as the winter gets colder.