The blue lights on your charger give an indication of the life left on your unit. You can recharge your charger at any time; you do not have to wait for all the lights to go out before charging.
To charge your charger, simply plug the micro-USB plug of the cord into the 'IN' port of the unit. And then insert the USB plug of the cord into an AC adapter or directly into a computer USB port.
The Visa + chargers takes just over 5 hours to be completely charged from zero. The Visa units takes just over 3 hours from zero.
Leaving the chargers plugged in after charging does not harm the unit.
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