Do you mean you turned the ignition to the on position or you had the engine running at home when you saw it was being drawn down?
1. Are you sure you're charging?
2. Many electronics, i.e. Fish finders, radios, GPS etc have memories & will draw some power even though you have them switched off. I had to put in some isolation switches.
3. Did you check every wire for fraying or cracks, etc? Did you pull fuses from holders & check for corroision?
4. Call Hank
Tom B.
(LongLine)