PD or Iota for my upgrade?

I see no need for lab conditions to determine if the PD can output rated current into a RV battery for more than a split second.

The amount of current the RV battery will draw depends on a few things, like depth of discharge, battery make and model, battery temperature, battery condition, wiring to the battery and probably a few more things. How the heck can these things be held constant for multiple tests without a highly-controlled environment? I'm hearing that with a resistor the nature of the load is important, and with a battery it doesn't matter. How can a PD converter be capable of driving a resistor at full power indefinitely, yet go wimpy when there's a battery there instead? There would have to be something about the nature of the load that negatively affects the converter. I can't image what it is, or how to figure it out, but wouldn't mind learning about it.