And now I have a battery box to power the radio box. This was a much simpler build than the radio box. It's just a 15 AH LiFePo4 battery in a plastic ammo can with fuses, a power switch, and a voltage display. I added a switch to turn off the voltage display. It doesn't draw much (the datasheet says 12 mA), but it's bright and redundant with the display in the radio box itself.