Check low battery behavior

[bigjosh]

Should 3 red blink and then sleep until button press

[bigjosh]

Currently 2 red blinks. We need to empirically adjust the cutout voltage.

[bigjosh]

Lowered threshold to 2.45V. We cna lower again once we get confidence that everything else is working.

[bigjosh]

Note that currently threshold is set to 2.2V but still seems to work fine. We need more physical units and more hours to confirm this does not cause problems.