There are 2 choices: 1st is connect direct to battery and have the USB live all the time or, 2nd: connect white wire to the Key acc. so that it turns off. I cannot see where the white acc wire connects near the battery . . does anyone have experience of where this is?
Always best to go with a switched live. Accessories such as this will likely have a small parasitic draw on your battery when the bike isn't running. I don't know the Monster but is there not an accessory socket under the seat that you can tap into the back of? Or even a sat nav connection up near the headstock?
The USB socket in the tray under the rider’s seat is pretty useless. You could use the plug from that to give you a switched live. Andy