My 3 year old BMV 712 Smart battery monitor is reading 0.3 volts too low. It reads too low at the main and auxiliary batteries by the same amount. I have checked the fuses. I have checked the connections. I have measured the voltage at the B1 and B2 terminals and the ground on the shunt. I have inspected the connections on the back of the monitor and on the shunt. My voltage is verified by the readings on my inverter, solar controller and hand held meter. All 3 are the same except the 712 monitor is 0.3v too low. What do I do next. If I had a spare cat5 cable I could try it.