I had a power cable hooked up, but I removed it due to some issues. I recommend using an SAE battery charger connection direct to the battery, an SAE to USB converter (preferably 2.1a) then a good heavy duty charging cable from there to the phone. This is what I had in mine and it did work well, when it worked.
Recently I pulled it out since the Tecmate 2.1a SAE to USB converter I bought cuts off below 12.4v and my lithium battery would often drop below that when cranking the motor (crossplanes take a lot of cranking power). This would leave me with no power and I'd have to pull the seat off to unplug it and plug it back in. I plan to get a new BatteryTender 2.1a SAE to USB converter that doesn't cut off in the future.
What I liked about this is most of the connections are protected inside the bike leaving just the end of the charging cable. I have Renthal clip ons so I just put the end of the cable down the right clip on to protect it when not in use. Another option I may try is getting a longer phone charging cable and hook up to the SAE connection I charge the battery with that's in the storage compartment.
[Blockierte Grafik: https://lh3.googleusercontent.com/-kTeqzwwCmlw/ViwS1wZ-uuI/AAAAAAAAvtc/o5_RT-DRnQgsSR3kaPfO1ABqES2R6L3AgCCo/s800/001]