Independently from hacking the LiFePO4 power module, I decided to try and make a small module with a soft power button on it — the same I linked two logs ago. I will use a thin PCB, so that it can be inserted between shields.

The schematic is based on several designs from various forums — I'm not smart enough to figure it out myself. Pressing the button switches the power on and latches it. Subsequent pressing of the button does noting, except pulling the GPIO4 down to let the Raspberry Pi know that we want to shut down. A long press (or pulling the GPIO4 low) forces it off.

It's a little bit more complex than I'm comfortable with, but we will see how well it works.