A single lead-acid battery cell produces approximately 2.1 volts when fully charged. Stack six of them in series, and a fully-charged "12 volt" battery will show an open circuit voltage of 12.6. Does that sound familiar? If your battery will pass a load test (no, there's NO substitute for a proper load test) - - - - -find somebody who can test and repair your charging system. Like the motto Sun Electric Co. used to put on all their test equipment- - - -"We test, not guess!"
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!