How old are the batteries? If your charger has these functions I would equalize then desulfate and see if that makes a difference. You can also take your batteries to Walmart or most auto parts store and they will run a load test to tell you of the condition of the batteries. You need a certain minimum CCA to turn your eng over which is higher than a gas engine. Someone with a DP can tell you that. For example my 454 needed 700 CCA to start it was turning over slowly and when I load tested it it had 500 CCA, so it was replaced with a battery that had 810 CCA.
