Why does my iPhone battery go down so fast?

I have the 4S. I know the 5 is bigger and has 4G of course, but there are speculations the battery life is worse. My iphone has all of a sudden been going down fast just by being on standby. I use my phone regularly, everyday. I've had it since last march. Lately it goes down a lot on standby rather than when I'm actually using it… Why is that? Is there a way to save battery a little more without
1.turning it off instead of putting on standby
2. Buying a mobile charger ( already have that)
3. Shutting down apps (not really effective)
4.getting new phone
Anyone have this issue with the iPhone? Other than that in my opinion the 4s is still amazing to me to this day aside from battery life.

If you are in an area with bad reception your phone always checks for good coverage which drains the battery alot oterwise maybe try turning the brightness down and also if you use big apps like black ops zombies they tend to drain the battery more.