Why does my iphone 5s battery power drain so fast recently?

So within the last 2 weeks I've been noticing that my battery power has been going down a lot faster than it normally did. In the past 5 minutes it went down by 5% and seems to be draining even when I turn it off. I haven't updated it at all and have only had it for 4 months. Does anybody know what's wrong?

Remove the battery and clean the contacts both on the battery and the phone. Use a Q tip or a pencil eraser. Blow out any residue or eraser dust. Let the battery/phone run down completely until it shuts itself off. Then, with the phone in the off position let it sit and recharge until is indicates the charging is complete. Once on see if you have a lot of apps open and running. If phone continues to run down quickly then you may need a new battery. Iphones don't have great battery life, that's why I went with/Android.

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