Vanleigh started using the PD4575 with the battery selection switch that is accessible from the front panel on 21 models. The next prior PD4575 had a jumper for the selection once the panel was removed and previous to that folks were updating their converters. I do not have specific experience with this just the research I had done as I went down the route of swapping to lithium. I am sure somebody else will jump in with relative info but this will likely give you some direction.
Pictures from the front of my Progressive Power Center.
