On the F800GS there's the CLC04BS which goes into your power socket and simpler solution.
As I recall, the Q~Power instructions say..
The cable has a bare wire end leads with an in-line splashproof fuseholder for connection to the motorcycle or scooter power source. It is recommended that the red positive wire ( +ve ) is connected to a point in the motorcycle electrical system, where there is power only, and when the ignition key is switched on. An example is the fuse box wirelink to the lights circuit.
Please follow following steps for installation:
► Remove the seat and find your positive red wire ( +ve ) connection point.
► Find a suitable place to attach the black box power case, making sure it will not obstruct the seat mounting or seat, when closed.
►Attach the black negative wire ( -ve ) to the motorcycle frame by finding a suitable screw or bolt, or by using a spade terminal.
►Attach the red positive wire (+ve ) to the chosen connection power point.
►Using the adhesive fixing pad supplied, peel off and place one side onto the black box and attach the other to an area under the seat. Be sure to clean any dust or grease from the surface before applying the glue adhesive patch.
►Run the output cable with the right angled mini-USB connector under the tank or along the side covers, depending on the motorcycle or scooter model.
►Be sure that you do not run the output cable too close to the engine head or near to any other engine or exhaust heat source. It is suggested that you look for and check where the main electrical harness of the motorcycle or scooter runs along and follow it. In some instances, you may have to lift the fuel tank to achieve this. In the front area of the motorcycle, try to run the cable together with either the cable harness, clutch or brake cable, making sure that when you’re steering or turning, the Q~Power Lite cable is not stressed.
►Once your output cable path is defined up to the gps or similar device, then make sure any excess cable not needed, is stowed away under the seat.
►The Q~Power Lite output cable can be attached to the cable wiring harness along the way back to the seat area if required, or be kept free (on scooters) and stowed away, when not in use.
►Insert the mini-USB connector into your GPS socket for power charging to start.