Modded the lefthand piece of the model to accept this USB charger module. https://www.amazon.com/gp/product/B09W48M3SG

You can print this and the original stem for a bike light, or this and the included modified end piece to just have a USB charger without light stem.

Bottom cap screws are M2x8mm

The module runs off 12v or 24v. You will need a buck converter that can handle your stock or upgraded battery voltage.