You absolutely have bad batteries. None of the batteries after charging should be as low as you stated. click on the link provided here and follow the chart across for 8V batteries. Your bad batteries are causing the charger to never shut off. Dont mess around, suck it up and go buy all new batteries at once, dont start doing half *** job and try to put in one or two batteries.
http://www.buggiesgonewild.com/elect...-readings.html