I think Keith has given you a good set to tips to find out what's wrong.
If you have a digital voltmeter, I'd go with this test; charge the battery, then release the clamps to disconnect it from the van. Measure the voltage - it should be very close to 12.6 Volts.
Then leave disconnected for a week or two, measure the voltage again. If still very, very close to the original reading, then it's looking OK.
If the volatge has dropped to 12.4 V, then that's equal to only 75% charged. If it's dropped to below 11 V then it's flat. These indicate that the battery is self discharging, it's dead and needs replacing.
If the voltage hasn't dropped from 12.6 V, it's time to reconnect the battery black pole, switch the meter over to Amps - and measure the current flowing between the red pole and the red clamp. If around 1 or 2amps are flowing, then something like a light is on. If 10Amps or so is flowing, that sounds like the fridge.