Buy an 80 amp boondocker that goes to 14.8 volts. Save your old converter or install the boondocker close to the batteries and run 120 volts to it. Charge time depends on how low your batteries get. If you are down 100 amp hours in the am it may take 4 or 5 hours. You may not reach 100 % in that time but close. The heavy amps will go in at first. As the amps drop ad the volts rise the end part of the charge can take a good deal of time.
A good battery charger will cost $400 plus, a good converter like a boondocker will cost $250ish.
What model converter do you have? Problem with some converters like wfco is that they only go to 13.6 volts.
