Question for you vets. I have an old Beaver Contessa (1990). I've had it for many years and never a (major) issue. I just installed (2) new battery's and I recently took a 250 mile trip with zero prob...
After one week, your chassis battery should still have held it's charge unless you had something that was left on and drawing power. I would use a meter to check how much current is being drained from the chassis battery when it is parked. Then you can pull out one fuse at a time to see which circuit is drawing current and discharging the battery.