I apologize if one of the previous answers mentioned this. But I believe the purpose of an MPPT controller is to charge your battery. Depending on the current state of charge of the battery the controller outputs different voltage and current levels. Sending 30 volts to a 12 volt battery is bad. The MPPT converts the input voltage that exceeds the desired output voltage to extra amps. What you want to measure is how much power (watts) is being transferred into the unit from the panels and how much is being transferred out of the unit to the battery bank. Remember P = I * V , watts = amps * volts. What is sent to the battery will change during the different phases of charge, bulk, absorption and float.