Default Completely dead N7, help needed.

A friend has given me his 2012 Nexus 7 because it wont switch on.

I read many solutions on how to fix this but nothing works. I'm getting no responce from the device at all.

Heres what I've tried:
Leaving on mains charge for over 24 hours.
Long press on power button (30s+)
Disconnect battery cable & re-attach it.
Un-plugging & re-plugging in power & then trying to power it on.

Theres voltage going through the usb socket & I've measured power at the battery connector with my volt meter but its not powering up.

Now I've read that the Nexus 7 normally has a 5V/2A mains supply, however, I'm only using a 5V/1A supply which I use normally for my phone. Could this be why its not powering up as its not getting enough voltage to kick start it from being completely run down?

If its not the mains power, any ideas what could be causing the problem & is there any way to fix it?

Thanks.