[cabmandone]

If the truck runs after jumping, the alternator is charging IMO. If the alternator wasn't charging the truck wouldn't run because the computer wouldn't be seeing the voltage it needs. My money is on bad batteries. If he has access to one, have him put it in alone (what I mean is don't connect the other battery). The truck shouldn't need two batteries to start in a warm climate and if the other battery would have a bad cell it might drain the one new battery installed.
BTW, if it's like most Ford trucks it has a system check feature. If he gets it started he can run the system check and if the truck is seeing normal voltage, drive it home.