BFL13- My clamp-on amp meter is fairly accurate. I have 2 other meters to check it. Plus I have a Xantrex Battery Monitor which gave the same voltage and amps that I read with the clamp-on. It's new and I do know that the cable from the controller to the batteries are 2x1.5mm which equates to 2 wires of 15awg. I ordered 10awg tray cable for my extension. Should be interesting to see if there is much of a drop. I could always change out the cables from 1.5mm (15awg) to the 10awg and see what happens.