Document that one can't flash with completely empty battery
I've seen
uuu (Universal Update Utility) for nxp imx chips -- lib1.4.193
Success 0 Failure 1
1:7 3/ 4 [Bulk(R):LIBUSB_ERROR_NO_DEVICE ] FB: flash -raw2sparse all librem5r4.img
more than once and always wondered why I would never see this.
Short answer: because I use my device too much.
Today I wanted to flash a device that had a completely empty battery and wasn't in ship mode so when pressing poweron + vol-up and inserting a USB cable it would show up on the USB bus and start trickle charging but flashing right away reproducibly gave above error. Not that it doesn't happen right away, it starts flashing a bit then the above error shows.
Starting over and having it charge for 30m was enough for flashing to succeed (after flashing and rebooting it's now at 3% battery so it really just needs a bit of charge to not draw too much power from the hosts USB). Might make sense to add that to the docs.
/cc @mladen @joao.azevedo in case it matters to support.