Hi Stefan. I would say max. 2 x 1.5 PET bottles. I recommend that you take lots of 0.33 or 0.25 PET bottles so that you can make full use of the small space. The same with fruit, snacks etc., rather small "objects" that are not bulky, then you get the maximum out of it. There are four of us and it was more than enough for us. The battery lasts 2-3 hours at maximum power, otherwise you can switch to half power. In the meantime, I have bought a second battery. The power supply is ideal: in the car, normal mains and battery.