The built-in charging cable is not replaceable due to its interface being fixed. However, we have done many tests which indicate that the cable will not be damaged, even after 30,000 times of use. Unless used strenuously, the charging cable can be used for more than three years guaranteed.
a. You are required to have your own power source; b. Connect your power source with the built-in USB cable from the backpack compartment(if you don't know the place, please take a look at the Kickstarter page), and please make sure your power source is on; c. Your power source is set! Just plug your USB cable in the backpack/duffle and your phone will get the power charged.
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