Dirty battery cable connections would be my first check. No, "They look good" is not the right answer. Remove both battery cables, shine up the battery posts with a wire brush, and scrape the inside of the cable clamps clean with a pocketknife. There's also a specific tool for cleaning battery connections that combines a male and female brush into one tool at virtually every auto parts store.
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!