When i installed my js alternator 300 amp in my 08 jeep wrangler my voltage at idle was 14.25v. I checked my idle voltage a couple months ago and it was 14.75... Now today and it is 14.85 to 14.91.. I know my agm is weak and needs replaced.. Can a weak battery cause overcharging? I am getting ready to switch to a headway bank and don't want to overcharge it.