Replacement battery not holding charge when off Power adaptor

All

I replaced the battery on my Mac at the end of last year with an iFixit. There were no issues and the replacement went well. I followed all the instructions on the site and was very happy with the result.

I have now started having issues with the battery staying charged and the Mac working off the power adaptor.

The battery percentage drops quickly and then the Mac will turn off after about 20 minutes. When i try turning it back on it shows that the battery is flat.

When i then plug in the power adaptor, the Mac will start but the battery will already show a high charge percentage.... it varies but between 30 - 60%

It will then stay at that percentage and then all of a sudden jump to 100%.

If I then unplug the power adaptor i get the same result.....