I will get to it later, why I removed my Garmin GPS and mounted a tablet instead, but that lead to a need of more USB-charger ports to my bike. I have a cigarette lighter port, but it has been unreliable and the need of one more extension cable is not desirable. I bought a USB-charger port, little less than 20€, and connected it to the battery, with a fuse. I soon found out that it draws current continuously, logically, and if I'd forgot to remove any gadget from the port, it could drain the battery. The solution is to connect a relay to the circuit, and I took the control current from a cable that is routed to the ignition key.