You have a current draw in the vehicle that is draining the battery while it sits there. The usual culprit is the glove box light, the door bows with age to the point that the light stays on. If this is the case the fix is as simple as gluing a darn penny to the lid. If this is not it take a slow careful look around the inside of the car with the doors shut and see if any of the interior lighting is left on, I had a customer just the other day with one of the lights at the rear grab handles that was left on and causing the same problem. If there is nothing obvious then you need to either check it for a draw yourself with an ammeter or take it to a competent Volvo Indy shop and have them check it out.

Mark