MarkH wrote: ↑
Wed Mar 31, 2021 12:37 pm
But I understand that it maintains its full charge by being topped up from the HV and this happens when any of the doors or front or back hatches are opened.
Nope. Just like an ICE car, it is just draining the 12v when you open the door and the interior lights come on. If you close the door(s) or leave them open and walk away, it times out at just under 13 minutes and shuts off the 12v power. That includes power to the 12v outlets as well. If you do anything else during that time like open another door, the timer resets. The HV battery is not "on" during this time. While the 12v cycle is "on" a fully charged 12v battery which would normally read ~12.9v when resting will show ~12.5v when it is being used by the interior lighting and whatnot. Once that cycle times out, the voltage reading goes back up to 12.9v
If you turn the vehicle "on" as in: Push the button on the stalk and put the car into "Ready" state, THEN the HV battery will kick in to re-charge the 12v. The reading at the terminals will then be just under 15vdc.
So that means it will also recharge the 12v battery while the car is sitting in Ready State or Driving.
My question is, given that it can top up small amounts of normal discharge by using the HV, why can it not do a more complete recharge if the 12V becomes significantly (but not completely) discharged?
If the 12v battery is "significantly" discharged to begin with, this is not normal.
The HV battery CAN do a more complete recharge but the 12v battery must be able to accept it.
As mentioned already it can't keep up with a worn out or shorted out 12v battery.
Some people mention smelling "rotten eggs" and find their 12v to be really hot. The battery is not holding a charge and all the energy that is trying to recharge the battery is being converted to heat instead.
The battery might also charge to 12.9vdc but if left to sit, it may self-discharge over a short period of time but the HV will apparently come on once it reaches a certain threshold and bring it back to 12.9vdc without any other intervention.
This would explain why some people have reported that their HV battery has "mysteriously" discharged by a few percentage points overnight or over a few days time and then later the 12v failed completely.