want to add power inverter, usb ports

[jrf4865]

I want to install a power inverter (12 volt to 110 volt) so I can charge phones, speakers etc.... I have 8 6 volt batteries, how would i do this? i do have what i think is a power reducer, I have headlights and tail lights. All I really need is to add something with two USB ports but not sure of best way to do this.