A good tip for battery life, which I found here back in December (The thread is probably well buried by now though!) is to fully charge the phone to 100%, unplug and then use it till the battery is down to very low - below about 10%, recharge fully again, and repeat.....
I was having similar 'problems' that you describe at the time, and tried this tip... it kind of resets and 'trains' the battery!
I'm not a heavy user of the phone, but I do let apps update as needed, etc - I like them have full functionality all the time! I can now get upto about 48 hours between charges, but that of course will vary with use!
Hope this helps.....