The most important thing with a battery voltage meter is to know what is NORMAL for your system. It does not need to be calibrated to some military standard as long as it gives REPEATABLE readings. You want a permanently mounted meter, some place where you will see it multiple times a day.
• Know what is normal voltage when the batteries are fully charged and there is no load. (Immediately after a battery comes off of a charger the voltage is ABOVE normal. It will take some time (10-20 minutes ?) with no load to return to normal)
• Know what is normal voltage when your solar is putting out a good charge.
• Know what is normal voltage when you converter/inverter/charger is adding power.
• Know what is normal voltage when you inverter is on. (This will change over time.)
Once you know what is normal, then you will know what is ABNORMAL and can dig into things more !
