The battery is literally the heart of the electrical system. It even determines how well the generator/alternator operates. At least half the problems with charging systems I've fixed since the early 1960's could be traced back to battery-related problems and/or loose, dirty connections. Until I am sure the battery is good and the connections are clean and tight, I don't even begin to check out other parts of the electrical system.
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!