Why my galaxy doesn't save its battery?

I have been using Smasung Galaxy S3 since may 2013. Recently my phone is often frozen. And my phone doesn't save its battery for a long time. What do you think? What is my phone's problem? Can anyone help me? If I format my Galaxy will my phone work as it was working before?

Welcome to Android Central! If the battery doesn't last that long, you probably need a new battery. 2 years is a relatively long time for a battery.

As for the freezing, try wiping the cache partition: http://forums.androidcentral.com/sam...2-s3-tab2.html