Phone won't turn on after battery replacement.

Hello there

Today I replaced my iPhone's front panel (backlight issues) and battery (didn't hold charge very well).

Everything went smoothly, more or less, but when i put it back together it didn't start up. I suspected the new battery was dead, but even after charging it for an hour it didn't seem to change anything.

Then i decided to disconnect the power ribbon and try turning it on while it's connected to a charger, which didn't work either.

However, when i connected the old battery it had booted up properly.

Is my new battery malfunctioning or am i missing something else entirely?

Note - with the new battery in the phone doesn't draw any power from chargers