BFL you need the curves for your actual battery bank. That's similar to what I did with my discharge curves for my new AGMs. But it is a lot easier for me to get pretty close to a constant current drain to make curves than a constant current charge. So I made discharge curves. This way I can determine SOC for my exact batteries instantly using a volt meter, when at a known draw down amperage.
You don't have to follow the curve amp rate to get a reading - you can grab just a point off of it after just a short stabilization period. The voltage under a certain amount of amps draw or load is MUCH more repeatable and instantaneous than a resting voltage.
Also for the curves above, notice how a small shift in bank size (say due to loss of capacity between overcharge sessions) leads to a shift of many tenths of a volt which is a major shift in SOC.
Jim
