[G22b58]

To add a data point this is my observations:
I sat in my parked G22 MHEV, engine off, for an hour (preparing several routes for a road-trip) so I though I should try my new CTEK PRO25S in order not to discharge the batteries.

The observation I did not expect was: Both the 12V battery and the 48V battery was charging!

Configuration:
* The charger (can supply 25A) was connected under hood.
* Hood open (resting on the first latch).
* Car was "ON". Was using the navigation in iDrive.
* BimmerLink connected to OBD2 to monitor charge levels.

Starting point:
1) The hood open without charger connected, so the voltage in the 12V connector showed that the 48V system turned off (reduced from the normal 14.1V when the MHEV battery is used .
2) Connecting the charger in Normal (charging mode) and a current clamp meter showed 22A into the charging post.
BimmerLink showed charge levels: 48V=30% and 12V=58%. 12V battery voltage shown after a few minutes = 13.2V and 48V battery current= -2A.
(I had been using the car on 12V battery for a while, explaining the charge level.)
3) After about one hour BimmerLink repported charge levels: 48V=45% and 12V=62%. The current into the charging post under hood had reduced to 20A.

It seams possible that the 2A charging of the 48V battery corresponds to 15% (in the range of 65Wh). It could mean that about 8A of the input was used by the 48V system. It could mean that up to 4A (average) was used to charge the 12V battery.