what i don't understand is why some people expect and want to see 'Constant Amps' for a period of four hours
amps into a battery is the relation of applied voltage to battery resistance/acceptance
to maintain constant amps for a period of four hrs requires one of two things
either increasing the voltage to force the batteries to accept the amps
Or
a very large bank that is sufficiently low that the charger cannot produce the amps the batteries will accept,in other words charge them at 20 amps over a longer period of time
which we are All of us trying to avoid
i think the chart shows the PD 80 preformed as well as any converter could be expected to perform
anything better is pure cream
a battery is not a fixed resistive load
thing might progress to the point of slightly better readings in cooler weather with a shorter extension cord or running at 120v from generator power, or maybe not