I have a 20 a HQST mppt controller connected to 2 100ah chins in series for 24v. I have 3 100w panels in series. I am using this for my "back up entertainment" system but use it daily (tv,cable box, and indoor cell phone booster and 1 led 7w light.) Most all winter the solar kept the batteries charged but occasionally I would get an intense light flashing overvoltage message. my concern is damage to the batteries. It does not appear to stop providing current to the batteries according to my ali shunt monitor. I usually get nervous and disconnect the panels. I am waiting on the arrival of two more batteries to increase my bank so I can add my 5 cu ft freezer to this circuit of usage. I anticipated adding another panel as well. I guess my question is how do you balance the dilemma of not enough solar input on overcast days to too much on sunny days?