Phone doesn't charge while powerded on

Hi guys

So a bit of a tricky situation here…

So recently my phone dies pretty quickly. I have it charged to 100%, it runs for a while and at around 40% or so left, it would power off (but this is not the actual problem), or so I guess)

The problem starts here (Phone battery at 0%):

As soon as I connect it to a power source, it charges for a few seconds, then the “SONY” screen appears (is it trying to boot?) and then it goes back to dark… and it is apparently NOT charging further.

So I disconnect and reconnect to the power source, but then again, it charges for a few seconds, “SONY” screen appears, it goes back to dark and stops charging.

Repeat the game.

Another interesting thing that happened:

Sometimes I do manage to turn my phone on (at 1-3% of battery), but when my phone is turned on, it does not charge although connected to the power source.

Only after it’s turned off (by running out of battery or by turning it off manually), it charges for a while, and then as written above.

So.. what’s going on here?

A few things to mention:

1. I have tried connecting to a power outlet and to my laptop (same result, also laptop doesn’t recognize the device)

2. Power cable and outlets are fully functional

3. Phone battery I guess is fully functional, especially since I bought a new one and inserted it today

My next step would be a hard reset, but then again, it will never have charged enough power to do that

Now I essentially carry a brick in my pocket :p

Also, with already 4 years of “service”, it might be that my phone has pretty much hit its life expectancy.

Any guesses?

Thanks