2002 Venture - Alternator or battery?

How can you tell which one it is? The battery is still the original one in the van.

Is there a way to know for sure before spending money on a new battery but worse is the aggravation it is going to take to replace it myself.

thanks

If there is an Autozone in your area, take your van there. They can test the battery and alternator and let you know how each one is. If there isn't one in your locale, check the phonebook for other auto parts stores and call them to see if they offer that service.