So I have a 93 with glow in the wheel wells. Whenever I go to any event or anything I usually leave them on but not too long afraid of draining my battery. In the store the other day I saw the little 12v battery's that go in little electric scooters and stuff for a good price. I was wondering is there any way I can wire that kind of battery to my alternator so it keeps charging when I'm driving then all it does it power my lights when the truck is off ??? Or how long would the battery last just with the lights hooked up before I'd have to charge it back up

 

You can configure it to charge when you want and disconnect when you want. Basically the 2 batteries are wired together in parralel with the power lead being split by a solenoid that looks exactly like the one on your fender for the starter, and works the same way.
You can't use a fender mount solenoid though, it will burn out. The one you want is called a constant run solenoid.