Not sure what has happened when I soldered the boards, but I never really got them to work properly. I just spend an hour on reworking and cleaning a board, but I've must have killed the chip doing that. Before it was accepting the bootloader, but now both boards are completely gone.

One spare board from the first batch is missing the chip and I'm considering to remove everything what's on there, cleaning all the pads and try everything with a low temp solder paste and new parts. It still bugs me that everything is running off of the battery voltage on the arduboy.

Or I'll just slap a known Atmega32u4 board on there and call it a day.