The prototype for version 3 has arrived and been assembled.  When it was first assembled there was a problem where I accidentally ordered the inverting version of the comparator instead of the non inverting version, this was easily fixed by getting the correct comparator. There is also a very dumb mistake where the low battery LED is on when the battery is not low and off when the battery is low, this is not worth making another version it will just be a battery ok LED instead of a battery low LED.  There is also an unintended feature/bug where the LED starts blinking instead of turning completely off when the battery voltage nears the dead battery threshold. This is almost certainly because the battery voltage goes up when the battery becomes unloaded and the 20mV of built in hysteresis on the comparator is not enough to compensate for it. The prototype has been through one discharge and charge cycle but not been extensively tested.