My iPhone 5s battery life has become really bad?

My phone would last a day now i find my self charging 3-4 times a day
it has really become annoying why is this i always charge my phone over night and take it out in the morning and its battery life would drop from 90 % to 30 % in less than 4 hours not being used
could this be because of iOS 8 do i need to update or do i need a battery change i noticed it a day or so after updating
please help i bed of! And is it worth upgrading to and iPhone 6?
could it be a setting problem i have tried everything turning of brightness 3g etc

Added (1). *beg

Cool

Try a new battery.

Here is what I would do, as your battery probably is dead. If the contract is up, I would trade it in and upgrade to 6 on a new contract, since its basically a free upgrade since iphones 5S is worth alot. Otherwise take it to an apple store, its pretty cheap to have them put a new battery in, and it will be just like a new phone again.