Gadget Hero's USB Port Tester Charger Capacity Current Voltage Meter with OLED Display. This USB Multi-meter plugs directly into any USB socket or Micro-USB charger or cable. It displays on the screen the voltage, current and capacity. Acts as both a vol and amp meter. All three are shown at the same time so there is no need to switch between screens. It is powered when you plug it in so no batteries are needed. Back lit screen will let you see it in low light conditions. Will handle up to 3.5A which is more than enough to test any cell phone or tablet. The monitor is suitable for 0-2.5 Amps, and 3-7 Volts and has an accuracy better than 1%. It can also give you a rough estimate of the capacity of the device you are charging. Features : Displays Current (Amps), voltage and capacity (19,999 mah) Perfect for testing how fast a USB cable or USB power adapter charger is actually charging at Can handle charging speeds up to 3.5A (3,500 ma) and 3v-7v Store charging data in memory. Flashes to alert of low or high voltage issues Test using a USB charger, battery power bank or Micro USB Cable. Test your iPhone or Android phone