Discharging Battery, very wired behaviour

Hello all,

Okay i got very interesting and weird issue that i need help with...

I have an iphone 5s that discharge the battery very fast like the battery goes to 40% from 100% without me doing anything at all.

It gets even more interesting; It charges battery in general but when the battery discharges completely it won't charge anymore. I know the issue is not battery because i changed the battery 3-4 times and still doing the same thing.

Anyone knows what is the issue? Please help me....

Thanks alot!!!!