Important: our USB-A jack conforms to the commonly used wiring: the outer pins carry the supply voltage. We have tested many devices, all of them worked perfectly. But certainly there are exceptions with regard to the devices suitable for connection, which do not adhere to the common standards and, therefore, cannot be charged. We would like to ask you not to contact us in this case as we do not have solutions for all devices available in the world.
You can also use a commercially available USB buffer battery (not included) to provide an additional power reserve while cycling.
You can find buffer batteries online for purchase as "Power Banks".
You should choose a power bank that has both USB input and output, and it should permit charging and discharging at the same time.