Car wont start

What is your question?

I just replaced my alternator and we jumped it but it wouldn't start up I mean I could turn the key and it would crank but it would not start up. After we took the cables off about 15 min later the car went dead the lights don't come on or I can't lock and unlock the doors with the automatic lock I think it might be the battery but I'm not sure I know I need a new one anyway but what other reasons could it be

What makes this problem better or worse?

Nothing

How long has your 2005 Ford Expedition had this problem?

A month