by noseoil » Thu Sep 08, 2016 8:55 am
Perhaps I should have been more clear in my statement about the use of a simple volt meter for SOC. If the battery is at rest, has no loads or charge happening (PV panels in the dark, no lights are turned on, radios playing, etc.) & hasn't been used for anything for a few hours, a volt meter is a very accurate measure of state of charge.
I do understand that temperature, recent loads, charging, PV panels, a full moon or fondling your crystals can affect battery voltage, but if you want to spend more than $100 instead of $5 to find out that your battery is charged or not, be my guest. Basically, you need to have enough charging capacity to keep up with your loads in any given scenario where the battery is being used. If the voltage is down, you need a charge. If the voltage is up, you are fully charged. There are too many factors involved here to list, but a simple voltage meter or a good hydrometer will both tell you the same thing about the state of charge of your battery, as well as your charging system.
Again, I apologize for my gross oversimplification of this whole process & any misunderstanding I may have caused, but a lot of this stuff is over-thought, over-engineered & just too complex for most people. Knowing down to the mili-volt the loads & charging uses of a system will only tell you that you have more or less power than you need. I don't like to spend money if I don't have to, so for me a $5 voltmeter tells me all I need to know about my system & battery.