My iphone 3gs battery percentage keeps jumping up and down. For example, it was at 50% and around 5 mins later it went down to 17% then went up to 30%. It stayed stable for a while and then shuts down (I assumed it ran out of battery, but it was still at 30%) Today's the first time this happen. I brought the phone on the launch date. should I be worried? Should I take this to the genius bar? Thanks in advance for your help.