You basically lose power everytime you shut off they key.
This is slightly unrelated, but I used to make some nice power modules so that one could remove the PC from the bike and program it (like if you don't have a 50 ft cable to run from the computer to the garage). I could start that up again if anyone wanted it. Basically it's just power to pins 1 and 5 on the PCII, I don't know about the PCIII yet, but I'm sure I could find out.