My iPhone 3Gs turns off and on itself, again and again when I charge it, then it shows the battery sign but does not start. It all started happening after I updated my iOS. What should I do? How should I make sure that my data on my iPhone is not erased?
after you updated did you restore from a backup or did you set it up as a new iPhone? To be honest it sounds like your iPhone may have water/physical damage.
Change your battery this method will work