>>619578> Dont really need much power since it only has to start a small engine and maybe only once or twice a year.All batteries are not created equal.
It's not so much as question of power as of battery design; your van's starter battery is designed strictly for a high load over a very short period of time to crank the starter motor, after which electrical power is provided by the alternator, it's NOT designed for long term electrical power.
A deep-cycle or AGM battery is designed for low load, long term power such as for lights, laptops, radio, fans, etc.
The reason you're having issues with your hippy van's battery dying on you, is because you're using for the wrong purposes; it is ONLY supposed to be used for starting the van.
Get yourself an AGM battery and put together a simple power pack as shown up-thread or just buy one (pic related) and use that for all your camping related electrical purposes.
And it sounds like you probably ought to also buy a new starter battery for your van, as you've fucked that one up by using it for electrical power for your laptop and such and have overly discharged it too many times.