Brian - some details on that little circuit!
The circuit is a "LED Battery Voltage Indicator" circuit with Dick Smith's
Kit Number: K3118.
The circuit board is 25mm square and incorporates a variable resistor
(trimpot) that you use to set the voltage at which the LED changes from green to
red (or vise versa - depending upon polarity and your needs).
For a container I used a 35mm film canister cut to approx 3/4 length
(ie. discard the open end) so that the cap still fits in place (this can be
later glued on).
I drilled a small hole in the middle of the solid end of the container and
fitted a LED bezel (H1910) which holds the dual colour LED, epoxied in place
from the inside. Attach you LED to the circuit board with hook up wire to allow
for the above mounting.
A small hole drilled in the edge of the film canister cap can be used for
the power leads. I wired this circuit in parallel with my spotlight from the
rear of the cigarette lighter socket.
It is a bit finicky to set the resistor. I used a voltmeter and a partially
discharged battery hooked up to my light dimmer control. You may have to
slightly recharge your battery and try discharging again (with your light) a
number of times if you miss your cut off voltage - Using 11.00 volts for cut off
will give you approx. 30min on full power with a new fully charged 7.0Ah 12volt
battery and a 100Watt globe.
Hope this helps, and doesn't sound too confusing.
ps. I have also used two of these circuits as a charging monitor. The first
LED changes from green to red as the battery comes up to charge, the second LED
changes from green to red when fully charged and activates a piezo