FWIW, Honda's had a AC relay problem that was a battery drain. When the relay goes bad, it would occasionaly turn the AC clutch on with the key out. When bad, pulling the relay would make the AC clutch release audibly. Our Odyssey is a Vacation vehicle so for insurance I installed one of these Priority Start battery savers. It works like a charm. Obviously tracking down the problem is the way to go but if your in a pinch for time, This gismo works great. As soon as the battery drains to 11.7 volts, it automaticaly disconects the POS cable. Then just by opening the door (cab lights) triggers the auto rengagement of the pos terninal.
http://www.ebay.com/itm/Priority-Start- ... 27c048ba4ahttp://www.amazon.com/PriorityStart-12- ... 380&sr=8-2