If your charger doesn't go above 12.65 volts your batteries will never be fully charged. The charger needs to get to 13.2 volts as an absolute minimum and at this voltage it will take several weeks to achieve full charge. The reason for three state charging is to shorten the time to achieve full charge. If your charger were to go to 14.4 volts your batteries would be fully charged with 3 hours at 14.4. A three state charger would hold the 75 amps until 14.4 volts, then hold 14.4 volts for 3 hours then drop back to 13.2 to maintain them.
Regards
Jerry 4107 1120