When I have a high load on my system the battery voltage on the MPPT display will go down. It usually sits between 12.8v - 13.1v however if the load is high (it is currently on 8amps) the battery level will drop down to 12.4 or something. This will then go back up if I turn the load off.
Why is this? I am worried about discharging the batteries too much and ruining them.