I'm leery of the kits. In general, they all take 12 volts and turn it into 5 volts, but how good a job they do may affect the dashcam. My second unit, now relegated to rental car use, has a proprietary cord and just plain doesn't like anything different.
I prefer using a loose 12V socket and the cord provided with the dashcam. This powers and protects as intended by the manufacturer and avoids a mismatch.
I had tapped the overhead console light, but found the car uses both the hot and ground to control it. That's when I ran to the fuse box with an add-a-fuse connector. This piggybacks on an existing circuit without splicing or otherwise. You can select a circuit always powered or powered with the ignition and change your mind later. Believe it or not, a good ground is often more difficult to find.
When I let go of minimizing wire length, I found the easiest part is hiding the wires behind finishes. A soft plastic spatula or similar easily pushes behind trim, headliners and dash edges. A little time on the internet easily reveals the right way to remove under dash panels and a wire tie will keep a loose 12v socket from rattling.
One manufacturer provides a cord that connects to the OBDII and captures diagnostics. I didn't think much about it until I saw with a flip you can switch from ignition controlled to always on. I suspect you may find similar third party connector for accessory power.
As to how long and battery drain, if you find the dashcam drains the battery, I suspect its a symptom of a bigger and unrelated electrical issue.
Hope this helps and please keep us posted.