Replaced battery, no charge, no reception, no wifi

So I just replaced my dying battery with a new one only to notice it wouldn't keep a charge (works only when connected to power outlet and shuts down when disconnected).

There's no service or wifi as well.

I double checked and tested all the connections and when I replace the new battery with my old one (which still has some juice left) everything works fine.

So I'm quite sure this isn't a connection problem.

But what is it? Is it the new battery not working correctly?

I was expecting this to be easier and more troublefree than it is now.

Thank you for your help.