If you're at all handy with wires, you can buy an extra set of test leads for the meter, cut off the probes, solder a 10 ohm, 5watt power resistor between the wires, then solder the appropriate end from a servo extension onto the end. This will put an approximately 600 ma load on the battery, and you can read the voltage out. Depending on your battery chemistry, you can then estimate remaining life. Make it even more accurate by creating a discharge curve for your battery by starting with a fully charged battery and then plotting voltage vs. time as you discharge the battery with this setup. Laminate the curve and keep it in your field box. Now you can hook up the battery, look at the voltage, and see where you are on the curve.

Brad