All good replies, but you may also need in some cases a DC to DC converter, probably a 5 volt output as you were talking about USB.
If yes, there are some good little PCBs on ebay, with USB output sockets for very little money.
Something maybe like this for 3.5 amps at 5 volt:-
Entdecken Sie DC-DC step-down converter 120V 96V 84V 72V 60v 48v 36v to 5V 12v 24v USB po_lk in der großen Auswahl bei eBay. Kostenlose Lieferung für viele Artikel!
www.ebay.de
I don't know your level of knowledge in such matters, but I hope you find this helpful possibly.
The specs are as follows and are all DC, suiting just about any bike voltage:-
100% Brand New and High Quality
Small size, high current, easy to install, with precision potentiometer adjustable output voltage. High voltage, can be connected to the maximum 120V input voltage for electric vehicle buck, the maximum 3A current. Mainly used in electric car modification.
DC-DC buck Step down module
8-85V TO 1-30V Adjustable Output Default 12V 3A
22-120V T0 8-28V Adjustable Output Default 12V 3A
22-120V TO 12V 3A, 5V/0.5A Dual Output (Note: The default is no potentiometer, after all, dual output is a fixed voltage, not adjustable)
8-120V TO USB 5V /3.5A
The difference between them is the voltage model, that is, the pressure resistance value is not the same. The supplier has the right to update the product, please understand.
A5: 22-120V to 12V/3A; 5V/0.5A dual output (The default is no potentiometer)
Wiring port type:
Input / Output cable length: 20cm
Board size: 33x24x16mm(L*W*H)
Package Included:
1 x High Voltage Adjustable DC-DC Buck Module with cable
Andy