Battery draw down

[phatdaddy]

I need some help from the gurus on the board. 150 merc(94) when the boat sits for a couple of days, the battery is drained. I am sure it is in the outboard & not the electronics or cabin. i can isolate them. My question is what would be drawing down that much on the motor that would not be obvious( starter, trim, key switch, etc.) If you guys can shed some light, i'll be grateful.