prodigy p3

Amperage is dependent on the draw of the total of the brake magnets and associated wiring. Voltage to the brakes is controlled by the P3. Your battery condition will have little to do with brake controlling as the vehicle's alternator will be delivering power to the P3 and back to the trailer's brake system.

Tekonsha advises an initial voltage of 6 V and adjusting up or down from there. An improvement in electrical efficiency for the trailer's brake system can be had by wiring the trailer braking in a star configuration rather than a daisy chain, as most trailers are OEM wired. This helps to deliver more power to the brakes. An increase in wire size accompanying the star configuration will also help with maximum electrical efficiency.

With my two axle trailer which is 4 brakes I see about 1 amp per volt.

That is if the P3 is putting out 7 volts then with it in diagnostic mode you should see about 7 amps.

7amps is where my controller is set so full manual travel gives me 7 volts and about 7 amps.

Each morning before I leave I put it in diagnostic mode and check the amperage. 7 amps I am good to go.

I have a P3 and will see a variety of readings depending on what pressure Im applying. Generally from under 2 to around 8'. I have to admit most of the time when I'm braking I don't have my eyes on the controller but what's in front of me. I've had it installed about 2 years and am very happy with it.

Full power should be around 3 amps per brake.
It will be less if your wiring drops volts en-route.