question

The higher voltage could be a result of ambient temperature. AFAIK the IP65 automatically compensates for temperature during the charge process. My guess is that ambient temperature of your battery is well below 25°C.

It is in my house at 22°C, but I do not see how that would matter. We are talking about voltage measurements 4 feet apart on a #10 wire, from inside the charger to the clamps.

UPDATE: The app is still showing 14.86 volts, but actual voltage at the terminals is steadily rising and now at 14.75 volts. So, where does the voltage reported by the app come from? It is obviously not a measured output voltage.

@mkc, voltage drop at an 8' round-trip distance over #10 wire at 10A current, 12v nominal is expected to be ~0.69%, and your reported value is ~1%, so you're well within spec, particularly at a lower temperature. VC is reporting internal voltage as measured before the charge current "leaves" the charger.

I just checked a voltage drop calculator and the answer was 0.08 volts, nowhere near what I reported. The initial figures I reported represent a 3% voltage drop.

@mkc, 14.86v to 14.75v is not a 3% v drop. And the voltage drop calculator you're using is either incorrect or you forgot to enter round-trip distance; a 4' distance is 8' round-trip. Expected v drop at 8', 12v nominal, 10A current, 10AWG wire is 0.63%.

The calculator I used specifically said to input one way distance.

Also the point you are missing is that the voltage reported in the app is steady at 14.86 volts while the voltage at the terminals is rising, starting at 14.4 volts and now at 14.8 volts. The 14.86 volts cannot be an actual measured voltage.