Been having weird issues with battery and/or charging. I purchased a voltmeter that plugs into cigarette lighter and reads battery charge level and also state of charging system while running. It appears that my alternator is at times charging and at other times not charging the system - what would cause this? Diodes? Voltage regulator brushes are fine, belt is tight . . . . . I swapped out old battery with new group 49 battery - weird!