when should a powermax pm4b drop into float mode

The VEC has its uses but the Meanwell (BTW I bought mine from the same place that Niner got his) is great in that you can control the voltage and let the batteries acceptance pick the amps. IMO, if you don't have a VEC, the Meanwell will more than do that job and it works in very hot climates too (I've had mine running 24/7 in 108+F/42+C).