It depends on your batteries condition but at 13.6V I can charge my two 6V batteries from halfway discharged to a full charge in about 36 - 48 hours. At that time the charger changes to the maintenace mode (13.2V). If I use the 14.4V quick charge mode they will charge to 90% in about 6 hours and them take another 12 hours to fully charge at 13.6V. These times are all approximations and assume no devices are pulling current while charging. My batteries are fairly new, purchased late last year.