I decided that the only thing I would ever use the 12V power point in my RV-12 for would be to plug in USB power supplies. So, I figured, why not bypass the middleman and just install a USB charging plug?
It’s trivially easy to find a dual-outlet USB charging jack with the same form factor as the Van’s supplied 12V outlet. The only downside I could find was a constant 10-15 mA current draw. The USB power point is a switching regulator and an LED. Even after clipping one lead to the LED it still draws about 10 mA. Now, normally the 12V power point is wired directly to the battery positive terminal with an in-line fuse holder. It would probably take a long time for that 10-15 mA drain to make a real impact on the capacity of the PC680 battery in the RV-12. It would only be a factor if the battery were weak anyway — precisely when you don’t want any excess drain. Plus, the old repair guy in me just doesn’t like the idea of cheaply produced electronics left under power all the time, unattended in an airplane parked in a hangar. Just to be sure I could shut everything off, I moved the supply lead from the positive battery terminal to the switched side (inboard side) of the master contactor. Now I have USB power controlled by the master switch.
It may be that at some point I will want to plug in something that requires 12 V – like a tire inflator, for example. I plan to put some leads and small battery clamps on the old power point and keep it around just in case.