[Al Skierkiewicz]

The diode/current statement was correct. You are asking that a diode be placed at the voltage input terminals such that a reversal would cause the diode to be reverse biased and no current would flow. The downside of this kind of design is that the diode drops 0.6 volts when forward biased. In a robot when the drive system demands a lot of current, the battery voltage does fall and that extra 0.6 volts may make the difference between working and not working.