Battery Voltage does not read correctly on transmitter or MP

After I charge a battery and see that it is full with 12.6V I place it in My new Iris+. After boot-UP my transmitter reads 1.3Volts low or more (10.9-11.3) This is within a few min of charge and/or the next day. The MP software detects low battery from this number and does RTL on my missions. How do I get the Iris to send the correct data to the MP software and the transmitter. I tried changing the Pin numbers in the param section but to no avail. Has anyone had this happen and what is the fix?

You can calibrate the voltage sensor using the instructions at: