Adding USB to an existing Ebike

Hi There,

I'm about to purchase a new ebike and noticed it doesn't have a built-in USB port as my previous one did. I'm curious if anyone has experience or ideas about after-market adding a USB connector to an ebike? I'm not really experienced in EE, but some google searches revealed essentially I'll have to attach a DC-DC converter to go from the voltage of the battery (72v45ah) down to the USB voltage. I'm a little bit confused on how exactly to connect it to the battery line however. Would it require something like splitting the headlight line? I'm not really sure how to proceed, as the all-in-one solutions I've found are more for e-bicycles and not ebikes. If anyone could point me in the right direction of how to start working on this i'd appreciate it.

This is pretty simple. First, you need to identify the spot where you can get access to a positive and negative wire on the bike. Could be the headlight, could be anything else, also depending on where you want the USB port. And then you find out if these wires run battery voltage or a already stepped down voltage and, if so, what voltage it is. You will find USB adapters of different kinds. On some you will just put an USB connector to an existing 5V rail, some others (especially for automobile and similar needs) will run on 12V or 24V and bring their own DC-DC converter for 5V and some others will have a wider input range, i.e. 7V to 26V, and they will bring an own DC-DC converter for 5V as well.

I've built a 4s2p 18650 pack that fits into a fanny pack hanging off the front of my handlebars. Ugly but it works.
This pack runs my 5V headlights, 12v turn signals (with relay) and 5v rear brake light/turn signal combo - all controlled by the handlebar mounted switch.
I've added a meter to see charge state a DC to DV stepdown for the 5V LEDs and a charge/balance connector.

Battery tester: Opus BT-C3100 V2.2 Digital Smart 4 Slots LCD Battery Charger AA and AAA US PLUG
Battery charger: TP4056 Li-ion Battery Charger Module Board. MINI USB

Voltage Display (I added a momentary push button to engage so that it's not "on" all the time.
https://www.amazon.ca/SSXY-Voltmete...=2025&creative=165953&creativeASIN=B07M5LSXWP
XT 60 connector for Load/Charge
4s Balance leads

Pics: pack, meter with button added, flasher, flasher timing setscrew