It could actually be your alternator. It's pretty easy to check before you buy a battery. Just disconnect the negative (-) black wire from the battery and jump start the truck. While it's running disconnect the jumper cables, if the truck dies your alternator is dead. If not, check out the terminals on the battery if they have a lot of corrosion or are loose you may be able to just get them cleaned and reconnected. Then just jump it again and let it run for twenty minutes or so to charge the battery and try shutting down and restarting. If none of that helps, you need a battery. There's a very remote chance the main fuse blew, but I've never seen one blow even with the battery shorted.
