Auxiliary battery

[JonPaul]

What keeps this charged? The engine? So I can't run entirely in EV mode all the time in case it goes flat?

 

[kpetrov]

Not the engine.
Main battery is charging the 12V battery when the vehicle is on. When the vehicle is plugged in 12V battery is charged as well.
If you have an wi-fi module the battery is charged at 2pm daily as well.