The inverter high spec is 15V. But it starts to fault at less than that under zero load conditions, so it I don't think it is a voltage drop issue due to too small of wiring. I used 2 gauge wire with about a 5' wire run (10' loop). The inverter won't turn on if the voltage is ~14.8V or higher with no loads attached to it. It just immediately faults. It is an inexpensive PSW from a China ebay seller, I've always thought that it faulting at 0.2V lower than it's claimed high voltage cutout is a due to its cheapness. But it delivers good enough AC power that my LCD TV likes it, unlike MSW inverter power. My small PSW inverter doesn't mind the higher voltage, just the larger one.
I use the voltage sense wires with the controller so it sees actual battery post voltage readings for use in both setpoint values and battery status. I actually don't recall if I've put my multimeter across the battery posts, but I've hooked my laptop up to the controller many times and viewed both the battery sense voltage and setpoint voltages. It seems to be behaving correctly, it accounts for about a 0.1V drop.
