"Dont charge your Fitbit with a wall charger!!!!! " Sorry mate, but I have to send all Your precious THEORY into a rubbish bin. And all that with a PRACTICE test with an USBport multimeter. So that's the results: Charging device: Port idle/Fitbit Surge connected . USB Toshiba computer port: 5,19V/5,16V USB Dell computer port: 5,19V/5,12V