For all you gadget freaks, here's a plan for a simple voltage detector. The circuit will turn on a LED when a voltage defined by you is reached, say for example when your battery is down to 11.5V.
http://www.riverrider.dsl.pipex.com/VoltageDetector.pdf
Here's where you can get the IC.
http://www.solarbotics.com/products/ind ... rch_id=101
Bruce