I purchased one of the plug in volt meters with two built in USB ports. It appears to be built out of billet aluminum and very well made. It plugs into the 12 volt outlet near the phone charging mat. This make reading the voltage easy. It is interesting to see the fluctuation of the voltage during start up and while driving. Mine seems to vacillate between 12.7 and 12.8 volts once it is started and moving down the road. At start up the voltage will drop down to 11.9 volts but quickly jumps up to 12.7 or 12.8. I haven't tried the USB ports.