I would put money on it that there is something in the car that is constantly taking a draw off the battery. 5 days is nowhere nearly enough time to drain a battery without having something to drain it. I work at a subaru dealership and we let cars sit on the lot for much more than 5 days without starting them and we never have a problem unless something is taking a constant draw off it. Check to make sure the glove box light switch is working properly. Ive heard a lot about those and have replaced a few of them. Also the light under the hood. Sometimes these switches to shut those lights off dont always work. Do you have any aftermarket equipment installed on the car that is electrical? (Example: CD player bought somewhere besides subaru?) This kind of equipment can void your warranty if something electrical like that goes wrong. Check little things like that and if nothing comes up, bring it to your local subaru dealer and have them take a look. It should be covered under warranty if its isnt something that has been messed with by aftermarket equipment.