Resurrecting an old thread, but I wanted to add that Cinno's solution worked well. As long as you don't mind changing the batteries every 10 hours of screen usage with the engine off, this seems like the far cheaper and lighter way to go compared to using the Polaris harness.
I wanted to understand how this worked a little more so I found the wiring diagram and did some testing first.
Here is the diagram, with red lines added to show voltage flow when the engine is off. The "Constant Power Diode" keep the power flowing only to the PIDD and not back into the rest of the sled.
Here is the diagram, but with blue lines added to show voltage from higher voltage engine supplied power. The "Battery Power Diode" blocks power flowing back into the battery, so no worries about unintentionally charging the AA batteries.
I then hooked up the battery using some alligator clips and tooks some measurements.
- I confirmed that there was 0 volts on GRY/RD with the engine running. (Battery disconnected for this)
- With the engine off, 0.3A flowed from the battery into the PIDD.
- With the engine on, 0.0A flowed from the battery into the PIDD. No amps backwards either.
In short, everything behaved as expected and it should work well.