What did you use to check the alternator? A brand new battery dead after a 1/2 to 1 hour lunch? Sounds like you either have a major drain on that battery or its just a loose connection. If you have a 12 volt test light or voltmeter check the battery for a drain. Disconnect the negative battey cable and hook the neg test lead of test light or voltmeter to the neg battery post and the pos lead to the neg battery cable. Now with everything off and door and hood closed if it has a light there should be no light on test light or voltage on voltmeter. If it has a drain, disconnect the alternator wires at the alternator, then start pulling fuses 1 at a time untill the light goes out or voltmeter drops to 0. When it does look at that fuse and see what components are on that circuit and start testing them. First thing to do is put the fuse back in and hook up the battery and make sure everything on that circuit works, such as bulbs, etc.