Hi,
In order to use a Pi 4B in the Pi-Top a cover has to be removed from the Pi-Top leaving the remainder of the unit, which I referred to as the base unit. That is accessible and was part of the remit for adding a Pi to the DIY Pi-Top. The Pi4B works perfectly fine isolated from the PiTop.
All I want to do is replace the battery that appears fault but there does not appear to a feasible solution to access the existing battery. If this is not user replaceable then I will chalk this up as a lesson learned and seek alternative solutions to running a battery based Pi.
I can’t quite understand what you have tried from your question … you wrote “removed the Pi 4 front the Top and that works fine” … “front” - … do you mean “from” … what do you consider to be the “base unit” to be?