I have had a look back at some data I recorded last September when the car was below 20% indicated HV SoC.
The car was parked for 45 hours with an initial18,8 indicated HV SoC and 93% 12V SoC. The recording taken at this time showed that the 12V battery was being charged at the time the car was switched off. At the end of the 45 hours the display HV SoC had reduced to 17.1% and the 12V SoC had reduced to 79%. Based on other measurements I have taken more recently I would have expected a larger reduction in the 12V SoC, however the data also shows that there was an increase in the 12V battery total charging.
The car was then driven 8 miles in short journeys spread over an hour and a half with Car Scanner recording the whole time. At the end of this the HV indicated SoC had reduced to 14.44% but the 12V battery SoC had increased to 94%. The recording shows that the 12V battery was being charged while the car was being driven.
I have not yet located data at lower HV SoC, however the recordings show that the 12V battery in my car is being charged from the HV battery with SoC down to below 14.5% and probably lower, bothe while driving and when parked and locked. The only change in characteristics that I have found so far when the HV SoC is low is a reduction in the HV discharge current limit. At high SoC I see a limit of 800 amperes. The behaviour does depend on factors other then SoC. I have seen discharge limit reduction starting above 30% SoC and below 20%. In this case the limits recorded were:
SoC % Discharge Limit/ampere
18.88 793
17.10 766
14.44 717
