Is my iPhone 4S battery defective?

My 4s battery seems kinda bad. I have the brightness turned up to almost 2/3. I try to not keep my apps running. But it doesn't last as long as my last iPhone. Like for instance I lost about 10% charge in about 15 minutes and I was just looking at pictures. Not doing anything intense. Is my battery bad? If it is, should I send it to apple to get it fixed?

It could be just the battery display on the screen itself, or if you plugged it in to charge before it was below 20% battery it could also mess up the battery but either way you should bring it to the apple store at the genius booth and ask them

If its jailbroken, thats normal, but if not, you could try running the battery down until it shuts down. That is supposed to be good for the battery, so do it at least once a week, or more if possible. If that doesn't help, take it to an apple retail store and talk to someone at the genius bar. They might have you send it back to apple to fix, which may take a while, so have a backup phone to use while it is gone.