I doubt it's the battery that is causing the phone to not boot. That is unless it behaves differently when you plug the phone in. Did you do anything recently with the software that would have caused it to do this?

So I think my Note II N7105 is bricked and won’t boot at all without any warning. An 8500mah extended battery had originally took my attention but i do not know yet is there any point to buy it now. My phone is not under warranty now, will a new battery fix a bricked phone? Any help is appreciated.