Hi,
You could also try turning off your phone's GPS and WiFi functions (if you do not need them at the time and if they're on, as they use a lot of power, especially GPS) and see if your battery lasts longer. Also does the camera have a 'flash' option that maybe you can turn on/off depending on whether you need it. This also drains the battery.
Does it do this when you have the charger connected and switched on?
''If not'', then your battery is probably starting to fail and needs to be replaced.