I'll reiterate this.
The fastest SAFE way to recharge flooded lead acid batteries is to apply amperage however much it takes, to instantly raise battery terminal voltage to 14.8 VDC @ 20C. Fourteen point eight volts is continued until such time as specific gravity raises to 95% of original fully charged density (acid has pronounced lag/overrun characteristics).
Four GC220 batteries (440 ampere hours) can easily accept a 120 ampere charge rate as maximum battery acceptance. This is provided to give you perspective as to what is allowable and to be expected. Forty amp charge rate merely tickles 24 cells and makes them giggle. Great for power post maintenance, crying towel sad for generator charging.