Understanding Fast Charging The output of a charge is measured in amperage and voltage. Amperage (or current) is the amount of electricity flowing from the battery to the connected device, while voltage is the strength of the electric current. Multiplying volts by amps gives you wattage, the measure of total power. To make a device charge faster, most manufacturers either boost the amperage or vary the voltage in order to increase the amount of potential energy. The majority of fast charging standards typically vary the voltage rather than boost the amperage. Standard USB 3.0 ports output at a level of 5V/1A for smaller devices like wearables. Most phones and other devices are capable of handling 5V/2.4A. For fast charging, you're looking at something that bumps the voltage up 5V, 9V, 12V, and beyond, or increases amperage to 3A and above.