I have recently got an electric coolbox for camping and picnics. Since the Superb's 9V sockets are permanently on (rather than switched with the engine), I'm careful to not let it run down. But I do tend to keep it charged and drive electric whenever I can, which got me wondering - the coolboxes can use quite a bit of power and I'm told they can drain 9V batteries in a few hours if left on. In a ICE car the alternator continuously charges the 9V battery so this doesn't matter, but if I'm driving only electric, does it also charge the 9V or do I risk running the 9V battery down? In a long camping trip this probably doesn't matter as I would be driving on petrol, but I can often go weeks running the car on just electric with regular day to day and weekend use.

To answer the main question yes it does charge the battery. Pretty sure the car needs to be on as that closes the contacts to the 400v battery so will only charge when driving.

Also to be clear, the battery you are referring to is 12v like all other car batteries. Not sure where you got 9v from.

Oops yeah got confused there. Thanks for the reply, that's good news. And I would also assume the car needs to be on, not planning to run the cool box while at vehicle is off.

I might be wrong but I don’t think these cars have an alternator (unless they’re at the weird point with a Starter Generator + hybrid motor)

 

The 12V battery is charged from a DC to DC convertor which steps down the 400V to 12V to keep the battery charged.

 

This is only done whilst the car is turned on as the HV system is completely isolated when the car is turned off.

@ApertureSyes you are right. 

Although I think the HV system also charges the 12v whilst the car is off but it's connected to an operational / live charger?

1 hour ago, Patent said:

Although I think the HV system also charges the 12v whilst the car is off but it's connected to an operational / live charger?

 

This I'm not sure and haven't found a conclusive answer. It would make sense from a technical use case. But, some other decisions by VW (etc) have made this platform odd compared to others. Some of which make it a nicer car to drive. Gearbox for one.