How to figure out what electrical components are present.

Personally I know of no converter that was built in that era that isn't a profound "battery killer". Ferro-resonant out-of-control regulation of DC voltage that over time creeps up toward fifteen volts continuous.

It gets worse. These caveman specials use a huge ceramic resistor to bleed a few amps of charging current.

Select something that will charge a car battery size RV battery at 40 amps per battery if you do any serious boon docking that lasts more than a week at a time.