That is from one of my ugly graphs which applies to charging a 220AH bank with 70,55, and 35a. The ugly graph that more applies here has charging a 458AH bank from 50% with a PM3-100 mod and unmod and also shows doing it with 105a of Vector portables (3-35s at once)
To answer the later question, you can't tell the battery SOC while you are charging it from the voltage. If you have some "markers" to tell you where you are at with your usual procedure then you can be fairly close, but most of that is using an ammeter. It is dead easy with an AH counter such as the Trimetric has.
First marker is the SOC when it starts to taper, which you can get from my ugly graph. The SOC for reaching 14.5v is proportional to the charging rate so you can do ratios for yours.
After reaching Vabs and amps taper, with only voltages you will see a small diff between charger voltage and battery voltage due to some "voltage drop" on the wires. As current gets lower, the amount of drop shrinks till when the batts are full, no current flowing, both voltages are the same. You could make up a graph of that for yours.
If you have an ammeter it is much easier since now you can use my ugly graph to see how far along you are in SOC when the amps are down to whatever. I use the "marker" of 5 amps per 110AH of battery bank to be 90% SOC at 14.5v. So with four batts you stop the charge when amps are down to 20a and you will be near 90% SOC at that voltage.
Note again how that marker goes out the window if your voltage is only 13.7 To be accepting 20a at 13.7, your four batts must be at a much lower SOC than 90%. This is where the OP was getting mixed up interpreting how far along he was with amps down to 2% of AH capacity without considering what voltage the batts are at.
