Battery stuck at 50% or unknown after iFixit replacement

Last week I bought a new battery kit from iFixit. I completed the replacement last night, charged it overnight however the battery died within minutes after unplugging the battery as it only showed it had 1% charge.

Then I plugged the battery back in, now showing 50% charge immediately. I left it to charge, then completed a hard reset and the battery shows unknown battery percentage.

There is also an error on the android battery page: Problem reading the battery meter.

Note that the phone does stay on for a few minutes before shutting off.

How to best proceed?