The most common problem is a low-current leak in an alternator rectifier diode. Try disconnecting the big charging lead at the back of the alternator before you park the vehicle overnight and see if the battery stays charged. It takes a pretty sharp technician to find that problem, and most of the mouth-breather counter people at the parts stores don't know how to check an alternator properly.
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!