Check Battery Level
If your device won't charge from our battery's USB port, first you should verify the battery's charge level. For the V15 and V44 Batteries, this can be done by pressing the Power Button and checking the LEDs on the front of the battery pack - if all 4 LEDs are lit then the battery is fully charged.
For the V88, simply press the Power Button and read the Power Level Indicator Bars on the LCD Display. Six bars means the battery is full.
Turn on USB Port
Tapping the battery's power button is necessary to activate the USB output of the battery. Please make sure your have the device plugged in before activating the battery.
Try Multiple Cables
Make sure you do not have a faulty charging cable by trying a new charging cable. If you do not have another cable, you can test this by charging from any USB port to see if the device is charging.
Don't Trust Charge Indicators
Even if the device doesn't indicate that it is charging, it might be. See if the battery level rises over time. Oftentimes, devices recognize that Voltaic batteries are not their normal chargers, but will still charge from them anyway. Some devices that are particularly picky will only charge (or will charge faster) when powered off.
Try leaving your device plugged into the battery for 10-15 minutes and recheck the power level.