Comment Re:If you're worried about being tracked/viruses.. (Score 1) 119
You will wait quite a while to get a charge that way. The devices negotiate the charging current over the data lines. The default is either zero or 100 mA. Best to buy a purpose-made USB data isolator that negotiates a good rate with a built-in microcontroller, but doesn't connect the phone to the charger data lines.
You can build one using a few resistors. See Adafruit's MintyBoost.