If it was ONLY the alternator, then why didn't it start after he charged the battery overnight? That suggests the battery doesn't hold a charge, or some connections are loose.

Loose big-cable connections can possibly cause all the troubles. This is true at both ends of all the big cables. Including the big ground from tranny to body. Or a bad alternator damaged the battery, and now has damaged the new battery too.

Charge the battery overnight, then turn on the headlights for 20 seconds to remove surface charge. Measure across the battery posts themselves with a meter, should be above 12v. Then turn on all the lights, fans, & stuff you can, don't start the engine. If it's still above 12v then your battery is OK.

If you can start it with jumper cables, measure the battery voltage with the engine running. It should be above 14v. If not your alternator isn't working. It should remain above 14v when you turn on all your lights & stuff.