Again, I am not using POE. I have a separate 2-conductor cable that supplies 12v to the camera. It's 4k so I need about 34-50Mbps from what I've read. How about this? Uses only two wires.
https://www.amazon.com/Ethernet-Extender-2000ft-Twisted-Copper/dp/B0BKPBQNKX
Those devices are a form of private DSL. Hard to say how fast they really run the longer the cable the slower they get. They talk about 92mbps maximum with less over longer distances. They do not even give a example of the speed at say 1000 ft which is half the distance. Makes devices like this very suspect.
You now have a additional box that now needs power. You likely already have issues running enough power over the thin wires used by ethernet you now need even more.
Although you say you are not using POE that is more of a technicality. You are still trying to obtain power over a ethernet cable, you are just trying to invent your own. There are massive issue with power loss over long distances.
Do you already have the ethernet cable run. Can you start over with another solution.
So best option is going to be to run a fiber than then use some kind of small solar panel and battery. There are massive number of security cameras that already have solar panels and you see this solution used all over the place for cameras they use along the highway.
If not consider running some thicker wire that will not get so much power loss at those long distance. There are charts that will tell you how much voltage drop you get per foot at different voltage levels.
I would still use a fiber solution no matter how you get your power issue solved. Fiber will give you full gigabit speeds and no issues with weather.