My iPhone 4S battery is showing charged sign even though its charged only 30%
Please answer my query
First, try to reset the phone by holding the sleep and home button for about 10sec, until the Apple logo comes back again. You will not lose data by resetting.
If this does not help, set it up as new device, explained here:
How to back up your data and set up as a new device
If still no luck, get it serviced: