I just built one of these devices, and it was not the easiest thing to get working. Apparently the diode is in the correct direction because it is charging our battery at a measly 10mA, which is not good at all, but I think I was using a bad battery. I had to substitute some of the resistors to other ones of very close value, like the 221 Ohm resistor (just try to find it at Radio Shack
) I substituted for a 220 Ohm resistor, so nothing major. When hooked to the robot I can run the camera from it without any problem, but if I add the backup battery and turn off the main switch/breaker, the back feed into the robot is horrible. All the spikes stay lit and the controller tries to run. I could not find an 8.7V Zener diode at Radio Shack, so I am going to order one of those. My voltage out hovers around 8.6 to 8.7 volts, and with the camera it drops to 6 volts. With the back feed problem, we may not be able to use the charger and a simple 3A diode that they refer to would work great to keep the back feed from draining the battery.