IPhone battery dying quick

I have an iPhone 4S and I usually let my battery die out about once a month. If I charge it sometimes and it's at 100% then if I unplug it the percent will drop to 96 or something. If I go out on 3G my phone will drop like 6% by doing nothing. Even if I'm not using it it will lose about 10%
I don't know what's wrong with it or why it's dying so quickly. Any help or suggestions?

Try to install new iphone battery original one in shop as i can't do alone its hard to remove battrry as its inside locked. Or back up your data and reset your phone but please take back up first. If its under warrenty then contact apple customer care. If chaging battery know abt your warrentu condition

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