Why is my battery charging slowly and draining so fast?

[AC Question]

I have an LG G Flex and for the past two days I'd have to leave my phone on charge for hours longer than I usually used to (I think it charged from 22% to 84% within a matter of 12 hours, and when I unplugged it it dropped from 84% to 62% within no more than 5 minutes. I drove to work and when I got there I was already getting notifications that my battery was low. I am not using a different charger or wall plug. Everything is exactly the same as it always used to be. I haven't installed any apps or done anything out of the ordinary to cause my phone to do this. I have noticed though, that the top part on the back of the phone (near the camera and volume up, down buttons) has become warm without me even using it... Does any one have any idea what might be happening?

 

[Tim1954]

Batteries have a finite life time, they have a number of discharge /charge cycles after which the chemicals deteriorate and the battery fails. I replace batteries at the first sign of trouble, to save me from an unexpected and inconvenient shut down..

 

[AlphaTango414]

I agree, it's time to replace the battery.