[Al Skierkiewicz]

Brian,
There is an alternative. It is possible that your battery somehow discharged through contact of the terminals or connector. This would normally show some voltage when checked with a voltmeter but not always. When the battery is discharged to this point, the circuitry in the charger does not recognize that a battery is connected and therefore does not turn the charger on. AS a last ditch attempt to revive, you will need a variable power supply and some method of looking at current. In this method, you would start out with a minimum voltage (1 volt) on the power supply while monitoring current. Connect the positive output to the positive battery terminal and the negative output to the negative battery terminal. Energize the power supply and monitor current. If it skyrockets (i.e.several amps) then the battery is likely shorted and it must be recycled. If the battery draws no current then it is likely open (internal damage usually from a fall) and the result is the same, recycle. If it draws some current then slowly advance the voltage without letting the current get over 1 amp or so. This step requires very close monitoring of the current and heating of the battery. If you can advance the voltage to 5 or 6 volts without running the current above 1 amp then let the battery charge for about fifteen minutes. Remove the power supply and measure the voltage of the battery. If it maintains some voltage above 5 volts, then try putting it on the regular battery charger. Charge for an hour or so and then test the battery in your robot. If it runs the robot for a few minutes, then you have been successful. Put it back on the charger and watch it periodically. It might take the full four hours to charge. Check for battery heating as well. If all is normal, then use it for practice.