Originally Posted by camaraderie
My guess on the OP is that the battery is effectively toast after being stored less than fully charged with low water for an extended period of time with plates possibly exposed.
NOTE that even with a voltmeter...you must first fully charge the batteries overnight...then remove the negative post cable for 24 hours. THEN take a reading to determine the true condition of the battery. Taking a volt reading shortly after EITHER using or charging the battery will give you bad readings. Anything read below 12.4V after waiting 24 hours should be considered damaged & on the last legs.
That is why the "C" stays lit until you put a good demand on the battery after you disconnect from charging power. Move the slideout and it will almost immediately drop down to "G"
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