What causes battery drain?

[rush91]

I keep having issues with battery drain. The car stays in a storage facility, so i have no access to hook the battery up to the tender I have. I have noticed that the battery slowly drains, which lead to the flickering of my dash lights..... I went to get the car out yesterday, dash lights were dim and i noticed the volts were nil before cranking. Go to start and nothing. So take battery out, its less then 6 months old, and run it up to AutoZone. They test it says yep it is low and charge it for an hour.... Put it back in the car and fires right up, no dash flicker.

Long story short, my question is what could be draining it? The car has a Viper aftermarket alarm, which i never use when i store it. Would it be best to just unconnect the cables when storing it?? Why i havent bought a battery disconnect switch is beyond me