I went out of the country for a week and before I left I shut off data services (just in case) and then turned the phone off and put it in my bag. When I got back to the airport (8 days later) and turned the phone on, the battery was at 65%. I had never turned the phone on during my trip.
I have a S1 purchased in December 08. Could it be that the battery is getting old?
Maybe yes. Try to charge your battery completly. After let it drain out completly until the bb wont stay on. It may take 1 day or more but after it drain out give it a good charge and see how it goes.