I have always liked tankbags and I always seem to have accessories that need to be powered, so the next step was to electrify my tankbag. I have a lot of bikes, so interchangeability and universality is very important.
My solution is a distribution box in the tankbag and a connection to a 12V BMW style jack located somewhere around the handlebar. The box has a cigarette jack, 2-2.5mm jacks and an SAE 2 pin connector, and a coiled wire with BMW plug to connect to the BMW jack. It also has a 15 amp fuse inside.
I don't use the radar detector on the WR250, but on my other bikes I locate the detector in the tankbag in the pocket that is in the lid under the map. I have a detector with an earphone jack and run a wire to a series of LED's in a small box on the windscreen. Lazer doesn't work in the bag, but I haven't found any Lazer, yet!
I've used this setup for the last 20 plus years, both in the dirt and on the highway, without any problems. I know that most people don't like a lot of wires hanging out of the bag, but the 2 or 3 wires isn't a problem for me. Another advantage is that most rental bikes have a accessory jack, so hooking up all of your electronics or charging batteries is really easy, especially outside of the US where they use funny plugs and weird voltages.
This one is on my KTM and is just one way of doing it. YMMV