Test Button - Jupio JDC0010 User Manual

USB
You can use your Duo Charger to charge USB devices while you're also
charging your digital camera or camcorder batteries. Plug the USB end of
the devices' charging cable into the USB output jack on the side of the Duo
Charger. The USB output is displayed on the LCD screen.

Test Button

You can test the charge state of your battery even with the Duo Charger
unplugged. Just slide the battery into the charger plate and press the TEST
button. Press the TEST button a second time to display the voltage of the
battery. After five seconds, the display will revert to showing the charge
state.
If the charger does not charge the battery, check to see if the battery is dead,
faulty or worn out. All rechargeable batteries eventually wear out after being
used for a number of cycles.