My mppt 100 20 Bluetooth app shows .70 to .80 volts lower than the actual battery volts. Problem arose today when the app was sending too many volts to the battery bank. Batteries were charging at over 15.4 volts and venting and hissing gas. I unplugged the panels. Removed the mppt from the power and restarted the unit.
Battery bank shows 13.76 volts checked with a fluke multimeter while the app shows 12.98 volts. 
