Most Uk sold Eriba's are fitted with a battery before sale, however many sold in Europe are not so yours may well be an import.
You seem to have looked in all the places where a battery is normally fitted so if you did not find one there will probably not be one fitted.
Zitat
I noticed that on the kitchen units there are 2 switches. One of them has an image of a battery
This switch is I suspect on the fridge and when connected to the car and the engine running (while towing) will power the fridge from the car alternator to keep the fridge cool in transit.
to the forum by the way.