Why is my battery acting crazy?

So I charge my phone up to 99%, unplug it and turn it off and go to sleep. When I wake up in the morning I turn it on and it's on 2-4%... this has been a regularity now. I also notice that when I unplug the charger and do some stuff ( open some apps and such) battery always stays at 99% while the phone is still on, it doesnt drop. I just got a new battery so I don't think it's a battery issue.

Forgot to mention it's Samsung Galaxy Core Prime if that helps :)

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