Just an idea of a modification for those who are happy with disassembly and soldering directly on to a board.
Don't attempt this if you are not completely happy as you are likely to damage the Pi.I wanted to get rid of the micro USB sticking out of the side and also fit a power switch. This way I can leave the plug connected all the time.
The switch is a latching push-to-make that I have recessed into the case (bottom right of case) so it doesn’t get easily accidentally knocked.
The +ve is soldered onto PP2 on the Pi so that the supply is still protected but it's not the easiest to solder to. You could us one the many 5v feeds elsewhere on the 2 boards to make the soldering easier but then you miss the protection.
I put the -ve onto the HDMI shield as it had a decent size tab with few tracks close-by. Needs a hot iron with a suitably sized tip as the shield sinks the heat.
That switch isn't the most suitable as they are not rated as high as I would like but realistically should be ok. I drilled the hole to the larger collar size and then just used epoxy to stick it in. I've left enough wire so I can swap it if it causes any problems. It only just fits under the ADS-B adaptor and with hindsight the switch could have gone 1mm rearward which would have been better. Alternatively just move the USB plugs around (2 and 3 instead of 1 and 4). The push button only just protrudes from the side of the case so unlikely to get knocked but the oversize hole makes it easy to access when required.
I removed the 2 USB signal wires and sealed them up. I retained as much of the shielding as I could. I soldered a replacement 24AWG silicone wire onto the ground as this was easier to run. Lots of little bits of heatshrink to ensure nothing can short in there. The outer shrink is a glued one and the hole in the case is a tight fit. This keeps it nicely secure but I also added a cable tie to prevent pull-outs. 24gague silicone wire also from the switch to the Pi. (20 won't be necessary for this internal wiring and would be very difficult to solder to the tabs)
Oh and decent quality 3M double sided foam to stick the pack on - but not on the removable Rosetta cover so you can still get to the ports (just!)
Small mod that hopefully makes it much more simple to use.
UPDATE MARCH 2021Cllick below link for a (possibly) unnecessary modification to improve GNSS reception when mounted upside down and with this battery pack attached.