"The Fastest Way" ?
Impress 14.8 volts across the terminals until the cells bubble lightly then disconnect.
With a single group 24 battery this may yield 40 amperes at max charge receptivity
With 6 cells of golf car battery this may yield 100+ amperes at maximum charge receptivity.
Note charging amperage when cells start to bubble lightly
Repeat as needed.
There is no other method on the face of the earth to charge an RV battery faster while retaining safety for the battery.
I have recharged batteries to 95% state of charge a minimum of 1/3rd the time an RV converter will take.
But with 2,000 watts ultimate charging amperage will be limited to around 80 amperes. This is fine with one or two car jar size batteries.
Temperature limits also apply. I would not charge batteries with the 14.8 volt absorbsion limit >80F