How to know accurate state of charge
Hi everyone, I have a question that I can't seem to find the answer to. I am new to solar. I read a few books, and watched hundreds of videos and got the courage to spend about $2,000 on building my own off grid system. I went with a 24 volt system. My question has to do with getting an accurate state of charge. I know I don't want to run my batteries down below 50% due to the risk of damaging them. The problem is how do I know when they are at 50% when there is a load on them. I have a chart that shows at 24.20 volts I am at a 50% state of charge. The issue I have is when I plug in even a small load of 100 watts the volts drop immediately to about 24.7 (or 70% state of charge). When I unplug that load it immediately goes back above 25.5 volts (100% charged). Anyone know of a battery monitor that has found a way to give an accurate state of charge even when under a load? I have a small system of 500w of solar panels, (4) 6 volt 235ah batteries, mppt Renogy charge controller. Thanks.