In addition to the good advice above, consider upgrading the wire size from your new converter/charger to the batteries. Often the voltage drop in that wire limits charging current. To achieve a voltage drop of less than a 1/4 V over a 10' distance from converter to battery, you need #2 gauge wire. Your original converter was probably wired with #6 gauge.
Do that and you may see the full 60A spec output. That should cut your generator running time significantly.
David
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