Understanding step down converters

[Drunkenclam]

Are you saying you want to use the cartridge batteries in your power tools (drill/saw etc)
to run the RV 12v systems? I suppose it might work, although hiw
long a battery would last running a 12v fridge, I suspect wouldn’t be for long, and may damage the battery (I’m no expert) but even when doing hardwork with a drill for a while the batteries can get a bit warm)

The step down convertor ratings are the max it can convert when given an adequate supply. I personally would give myself 10% leeway and not give a load of more than 5.5A.