I have had a 200# Spyker for 3 years now, never had a problem with it draining the battery. I use it up to 8 hrs a day for weeks on end. Mine are connected to 19hp and 17hp Kawasaki engines. I think you might have something else wrong. Have you gotten in contact with Spyker? Those guys are pretty helpful about this stuff. Like I said, no problems with mine.
Take care of your customers and they will take care of you.