@power46 There is a lot more to it, e.g. lead acid voltage drop under load, charge and roundtrip efficiencies etc. Maybe spend some time reading up on the various aspects as you also don’t discharge lead acid chemistries below 50% which all should be factored in when sizing a system.
A properly calibrated battery monitor can provide a lot of useful information such as SOC based on the power in and out of the battery and even approximate time-to-go. The Ah in and out it how you measure it. Have a look at the range of monitors here. If you have e.g. a LifePo4 with a bms and bluetooth, it is another way.
What I find very strange is that the controller shows a very greedy approach.
Consider the case the battery has very low voltage in the morning, even if there is sun for all day, most of the energy yield is done for a short period (2-3 hrs, battery voltage up to 14.6V), then it sort match the solar power to the load.
If I attach more load the solar power jumps up to compensate.
In a way the controller never really full charge the battery.
I am not sure if it is a configuration issue, now I have:
If the battery is full it will not take a charge and loads will be powered very much from solar. Your load is small so you never use the battery much it seems and it only gets topped up from what I can see. The history graph shows you a lot of detail or you can do as you did.
But if the battery is fully charged (even if considering a 50% efficiency 12*110/2=660Wh), why it can sustain a load of 15-20W for only 12hrs (16.30/4.30) circa 180-240Wh?
Use a multimeter to measure the voltage at the MPPT terminals and also battery terminals to see if it may be an incorrect V reading issue and I would not discount the possibility of a bad cells even. How warm does the battery get when charging?
