[Al Skierkiewicz]

joachimbean,
The 24 volt power supply will operate down to about 4.5 volts on the battery. If you haven't charged the battery, it is possible for the battery to fall to less than 4.5 volts when you try and power the robot. However, there is always the possibility that one of your batteries has been wired backwards. It happens all the time at the beginning of the season. Check all batteries with your voltmeter to be sure. The battery connector is marked with a + and - as well as the PD. Measure the voltage right at the input to the PD to be sure you have the correct polarity and a battery that is well above 4.5 volts.