If you are shooting with a Sony camera, you know that they eat and spit batteries faster than I eat M&Ms. One trivial options is carry another set of batteries (though originals are about $45 each). What I am doing is using off the shelf power banks to run the Sony for much longer than its original battery.
Here is the issue. The original sony battery is quite feeble, it carries only 7.3Wh of energy. One issue, is that 7.3Wh is not a lot of energy for video (and definitely small capacity for 4k). The other issue is that this gives you about 5.9Wh per dollar. It’s not horrible, but definitely not optimal.
The Anker power bank that I am using ($45) is 20,000mAh at 4.7V which stores about 94WH of energy, that’s a whopping X12 factor on the sony for the same price.
The only caveat is that you would have to get something to use that cheap energy inside of the Sony. And this is where the Case Relay comes into play. You would need two parts: a Case Relay ($99) and a battery dongle ($35). I am using the sony flavor, but there are dongles for other batteries as well. The combined costs of this bundle is just short of $200. In batteries this is 4.5 Sony batteries. So if you are planning on using more than 4 batteries, this is probably a better solution.
P.S. the Case Relay as a small internal battery, which means that you can keep the camera on while swapping power banks. If you ever get to that on a 12 battery equivalent pack.