Loses battery charge

My mother in laws 1986 Century Limited w/3.8L will loose its batt. charge after a week of sitting. We removed all mercury switched lights like the trunk and eng. comp. lights. The battery is new as is the alternator and the starter. No corrosion on any of the cables. I know the ECM will draw a little but shouldnt drain it in a week. We checked the electric cooling fan to see if it was coming on over night......any ideas???.........gofastpilot

What power options do you have?