Using an automotive battery charger when onboard fails

My "smart" battery charger will shut off if it sees a significant voltage drop after it goes to float made. It also throws an error code if I try to charge 400AH bank from 50% SOC. Apparently, it takes too long so the charger thinks something is wrong. Reset it enough times and you can eventually get the bank charged. Think the charger is too "smart" for use as a backup for the converter.