I assume you only have the one battery, Katy?
Irrespective, a healthy battery should more than cope with ‘phone chargers (a miniscule voltage) and a light + heater for one evening.
As I see it, the possible problems – either the charging system (vehicle alternator to battery via Schaudt Electroblok) is defective; you haven’t given the engine long enough running to charge up a depleted battery; a defective 240v-Electroblok supply to the battery if on site; or a battery that is on the way out, not holding a charge.
I’d check the battery first, the most likely culprit, if your use of it hasn’t stretched over several days?
Stop by a battery supplier or even your usual garage – they can run a test for you, of both the battery and the charging circuit.
I believe you ‘wild camp’ a lot, Katy? In which case I would seriously consider adding a second battery to your habitation set-up. If your battery is defective, then now is a good time to fit a pair, as they should be matching, in both amperage AND condition. With winter approaching, the security of having more than sufficient battery power is great.
My set-up consists of two 110ah batteries, with a Sterling B-to-B charger between the alternator and batteries. This means that the very minimum of engine running pumps the maximum power into the batteries, keeping them topped up on even very short runs. We normally have several lights on (for the pleasant ambience) a TV/DVD playing, plus heater, ‘phone chargers, etc., all running together with no problem at all. And for more than just one night.
Good luck and let us know how you get on?
Barry