OK, serious followup now:
Tonight I installed the USB power ports I mentioned up-thread, and mounted the unit on the handlebars.
The installation was not actually that difficult (I did see a couple of orange sparks at one point on the negative battery terminal, but I'm a big boy). Except, two things:
(1) On the negative terminal of my battery, the wire doesn't screw into the post. The inner (cubical) housing of the post, where the threaded holes are that grab the screw, is missing. So the screw on the end of the wire assembly basically just flops loosely through the big outer hole on the post, and is held in place by the pressure of the rubber cap and the tight seat of the battery against the back of the housing. Because the battery seats so tight, the connection is fine (in fact I wasn't aware of this until just now, and I've ridden almost 2000 miles). Do I need to fix it, or can I leave it the way it is?
(2) Routing the wiring is a pain. Why do they give you so much damn wire? I ran it under the gas tank (above the engine), cable-tying it to the wiring that was already in there (to keep it off the top of the engine), threaded it through to the underseat area, then clumped up the excess into a cable-tied packet under the seat just rearward of the battery.
But power is flowing to the bike, and power is flowing to the accessory, so as best I can tell, I did it right. And now I'm not scared of batteries anymore.
Rich