1984 Suzuki gs550e electrical problems help!?

ok so my bike runs GREAT! after a 20 mile trip and i park it the battery is dead :(. i know its not the battery cause its new, i know the regulator works because i have tested it and its putting it back in the battery around 13. i just dont get it i have to buy a new battery every year because my bike keeps draining it. i am suspecting its the headlight. it looks like someone put a "stanley" car light in the front maby its the kind of light that came with the model but i am so lost. i changed the sparkplugs i just tuned the carbs it runs great its just this stupid drainage issue..... please any advice cause im about to burn the bike. (even though i love it....)