Is it my phone or the battery? Help!

[LaBelleDameSansPatience]

Hi, I wonder if anyone knows more about phones than I do. (Probably almost everyone does ..)
I have a Galaxy Ace 2, about 4/5 years old. It started running out of charge after just a couple of hours instead of a couple of days as it used to be, so I just bought it a new battery from Amazon. The trouble is, it still runs flat after an hour or so and is therefore useless ...
Do I need a new phone? Have I just been unlucky and bought a defective battery? I really need to have a phone to juggle all the things I am trying to do ...

[chipsandpeas]

try using a different charger, if that doesnt help its prob a issue with the phone

[LaBelleDameSansPatience]

Have used two different charges - home and work - with no difference. Must be phone then. :(