I went for this method of replacing the SSD. It’s less stressful than trying not to break the screen.

I went over the FAQs and it looks like it measure current and know how much energy has passed through but I wonder how it handles if you plug in the device at a different initial charge.

That won’t work either, it needs a Bluetooth connection to know the phone’s charge which means the phone needs to be on.

It will only reboot once unless it is unlocked again https://grapheneos.org/features#auto-reboot

I have one too and it’s been great. They sell replacement parts including the rubber liner if you need one soon: https://www.litter-robot.com/litter-robot-4-globe-liner.html