I have routinely been using the Battery SOC as the trigger to start and stop my generator, and it works great, with one issue. As a long term off grid system that is a hybrid of generator and solar, the system can go several cycles without synchronizing the SOC function of the battery monitor. This has only a minor effect on the generator start function, but it can have a significant effect on exactly when the generator shuts down.
It would be great if there was an option to shut down the generator based on the tail current into the batteries. At a constant absorption voltage, this will result in a more consistent REAL battery SOC at the end of the generator run cycle than relying on the battery monitor which might be out of synchronization.