Clean and tighten the battery cable terminals. Works every time. The inside of at least one of the the terminals has enough corrosion to kill the current flow as soon as a little load goes on the connection.
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!