NielV It is just a sensor. You can use it with either TH10 or TH16 modules from Sonoff.

NielV You can modify it, I've done it with a different module but the circuit is the same. Remove D3 and connect 5V after it, and remove fuse R0 so that the switch mode power supply does not get mains (or other voltage) input. That's it. Or if you want to run it off 3V3, then you also need to change the relay to a 3V3 version and bypass the 3V3 voltage regulator U6 as it is no longer needed and you do not want to waste the voltage drop across it. If you do not understand what I said, then please do not try it...

NielV Irrelevant, it just looks for a difference of 0.1V and does not care about absolute voltage as long as there is enough to power the IC. The picture showing voltage is just indication of nominal cell voltages of a pack for your reference.

NielV i have not bought one, but as an electronic engineer it does look like a switch mode balancer that transfers energy from the higher cell to other cells rather than wasting the excess by dissipating it into a resistor.

NielV No, it takes digital Ethernet network cameras, not analogue coax cameras.

NielV 3000W / 300V = 10A. It is rated 20A, so max voltage at 20A is 3000W / 20A = 150V.

NielV I have not yet bought this cable, but there is only 1 photo with the micro USB connector pointing in an opposite direction and in that photo you can see the buttons on the phone are also swapped so the photo must have been mirrored when it was edited.