This didn't happen for the first couple of weeks I had the car as I drove it enough that the standard 120V OEM charger would barely have time to get it fully recharged by the time I used it again the next day. But I bought a level 2 charger that charges 3 times faster and now the charge is done in just a couple hours and the car sits plugged in over night, but already fully charged. I realize I can schedule the charging using the UVO function, but I haven't gotten around to that yet. I thought it was a problem with the L2 charger so I returned it and bought another brand/model, it does the same thing. I have even had this issue with the OEM charger if I drive very lightly one day and plug it in over night, the charge doesn't take long and then by morning the 12V is dead.
After the first time this happened the OEM 12V battery refused to recharge and my charger showed a fault. I am just outside of the 2 year warranty on the OEM 12V battery so I bought a brand new battery, but the issue still remains.
I have searched the forum but the only close matches I see are referencing the french forums and don't seem to have a solution to the problem.