90 econoline won't start on occasion

[tjadams]

i have a 90 econoline conversion van. it has all the extra's tv, tons of lights, two batteries, and it will completly kill both of them to the point it won't start. when it does this it can't even be jumped, but if i take the main battery out and charge it, it fires right up. it will last varying on how much it is driven anywhere from 2 weeks to a month, then you go out to start it and nothing. when it initially did this a mechanic jumped the solenoid and it started fine, but that trick doesn't work anymore. matter of fact the solenoid got replaced and if you even try jumping it you're going to get lots of sparks, and one fried tool. just recently upon turning the key the door locks lock, then unlock. though they don't do it all the time. the extra lights work when they want to, and the tv doesn't work at all, though i have no idea if it's getting power to it yet, as i have not checked. there is a master set of switches to all of the extra lights and the tv, which i keep off unless i actually need light in the back.(and that's if they happen to want to work at the time)any suggestions to what could be killing the battery?

[KimMG]

How many amps does your alternator put out? Are both ends of each battery cable clean and secure. Make sure the engine to chasis grounding strap is securely connected. Measure the resistance of each battery cable. Check the charging system. Check for a power draw.