I'd like to make a simple USB-C Battery Pack to provide extra charge to a video camera. To buy commercial versions of this can be quite expensive, so I'm wondering if anyone has ever endeavored to do this themselves and what it might entail. Is it as simple as connecting series battery supplies to the power pin of a USB-C port?

 

Plug a USB-C cable into one of these: https://www.ebay.com/itm/9V-12V-24V...e-DC-DC-Buck-Step-Down-Converter/223308042405

And wire it to almost any battery. Something above 5v.

https://www.ebay.com/itm/Zeee-50C-2...eans-Plug-for-RC-Car-Truck-Buggy/382906069499

Or, $40 doesn't seem to bad for a manufactured one: https://www.amazon.com/AUKEY-20000mAh-External-Compatible-Nintendo/dp/B0759TDR3H

 

The generic term I found for these devices is "Power Bank". They come in different capacities but are all basically the same. One thing I found when trying to power a microcontroller development board is Ppower Banks require a minimum load. Without enough load, they shut off after about 10 to 20 seconds. The minimum load on my Power Bank was about 100 mA. This is to prevent interface circuitry on a load which is always on, even though the load device is "off", from draining the battery over time. Cypress Semiconductor and others make Power Bank control chips and this behavior is documented for the ICs but not documented for Power Banks. Not a problem for most uses but, of course, it took up a few hours of my time figuring it out.