Here's the schematic for the battery voltage monitor:

http://img151.exs.cx/img151/7118/batterymonitor2dm.jpg

I'm using a Batteryspace 14.8V 4AH Li Ion pack that puts out anywhere from 16.8V fully charged to shutdown at 12V. I wanted something simple that would tell me the charge state of the battery at a glance. The monitor has a red and a green LED which will be mounted in the handlebar switch unit:

- At full charge the green LED is on and the red LED is off
- At 14.8V (approx. 50% capacity) the red LED starts to light
- At 13.8V both LEDs are on
- At 13.2V (approx. 10% capacity) the green LED turns off and the red LED stays lit

With a different voltage zener diode the circuit will work with other batteries, such as a 12V SLA. I will also incorporate a separate low voltage cutoff circuit that will disconnect the battery at 12V to avoid overdischarging the pack.

By my calculations I should get between 4 and 5 hours of running time on a charge with everything turned on, depending on how much I use the brake. If I turn off the LED headlight and Warp Drive, runtime should be around 10 hours.

Here's the battery and charger:

http://img57.exs.cx/img57/3056/batterycharger6nv.jpg

The lumpiness on the top of the battery is the built-in battery protection circuit board that includes overcharge, overdischarge, and overcurrent protection. Batteryspace says their low voltage cutoff is set to 2.5V which is too low for my liking so mine will shut down at 3V per cell.