In a van, camper van or motorhome, you'll have electricity in the cell at all times, both when driving and when stationary. The auxiliary battery will power the lights and USB sockets via a 12-volt electrical circuit. The auxiliary battery can be recharged in several ways: while driving (600 km for a full charge), using solar panels or by connecting the motorhome to the electricity grid.
The auxiliary battery is fragile. It is known as a "slow-discharge battery". You must be careful never to discharge it completely, otherwise it will no longer recharge, or recharge poorly. What's more, if you accidentally discharge the cell battery completely, nothing will work in the living area of the motorhome. So goodbye: lighting, telephone recharging, hot water, fridge (even if it runs on gas, the piezo is electric)... Take care.
You'll find 220-volt sockets in the motorhome, but these will only work if the vehicle is connected to the power supply (socket or electrical terminal).