Sweet 6 pound 8 ounce baby Jesus! That voltage monitor is an awesome idea!!!
EDIT: ok, I just noticed that they come in different voltages, make sure you buy a compatible one for the battery you get.
It plugs into the other wires that are already on the battery...
I'm going to give this one a try for $4, it can tell me the voltage for each cell (to balance them) and the overall total voltage.
http://www.hobbyking.com/hobbyking/...2_8S_Cell_Checker_with_Low_Voltage_Alarm.html
The one I posted should work just fine, it measures within the correct voltages. If you want to leave the monitor on the pack the whole time the more expensive one might be a little better because of the power saving mode.
Also I edited my post from above adding a question about how you charge your pack.
EDIT: Never mind, you saw my edit. Thanks!