"When you are connected to the battery, the unit's meter will show a variation of the "converter voltage" so when you want to set the "real converter voltage " with the knob you can use your marks around the knob."
To avoid the sudden rush of amps into the batts, could you not do a soft start by simply dialing down the pm's voltage to roughly match the soc voltage of the batts, and then slowly raise the voltage to control the onslaught of current until it's up and running at its current limit? (This would only take about 30 seconds of your time, initially.)