On the Fourth of July the battery level indicator on my iPhone malfunctioned. It consistently registered very high (close to 100 percent) throughout the day. This should have been a tip off for me.
I expected the phone to warn me that the battery is running low, and for the battery level to be reflected properly at that time. Instead, it just shut off when it had no more juice left, and I was left to wonder what happened. When I attempted to restart it, it said that there was insufficient charge to operate and shut itself off again.
I’ll have to look around the Apple iPhone Forums and see if this has happened to anyone else.