Originally Posted by L.B.S.
It only depends *how* the power is going into the GPS unit you may have, that's all.
All USB/mini USB ports are 5V
With my Nuvi 765T, I bought a cable that had bare wires on one end, and the appropriate Garmin plug on the other. Not for the mini USB port, but the larger multi-pin connector that goes through the mounting clip.
I bought the OEM BMW accessory GPS adapter plug from F800Depot, and soldered the proper wires together. Works like a charm, no 5Volt thingies need apply.
Now, if I had another model of GPS where there was only a 5V mini USB power plug in, or for some strange reason I wanted to put the power to my GPS through the mini USB port, this is where you would need to make sure you had the correct inline voltage reducer.
I chose to go this route instead of just hardwiring directly to my battery, because I already have a Battery Tender SAE pigtail wired up to the terminals and I don't want to overcrowd the thing. (and I don't need or want to install a secondary multi-accessory fuseblock) Plus the GPS power source plug was already there, so meh.
Thanks - clearest answer I've seen. The point about crowding the terminals is a good one. I've got pigtails on both bikes, more for running the 12V air compressor on the trail. The 690 has no handy accessory plug and the wires on the Garmin adaptor are super thin, so I'm going to go that route for now and carry extra terminal screws. I'll get the adaptor for the 800.