I have a problem with my iphone 3gs.It switches off randomly while using applications and has to be plugged in a source to switch it on again and when it switches on after 2-3 minutes the battery is just 2 or 3% less than when it switched off like the phone switches off at 70% then when it is turned on it is around 68 or 65%. Any idea what can I do??? My iphone is on ios 5.1.1
Sounds like your battery is dying or has a problem - since it switches off when more than standby power is needed.
You can change the battery but I doubt that it will be cheap ...