battery or alternator

Hey Fellers,

Last few days my '92 SVX has not been keeping the battery charged up. I haven't been driving it much but it is kept in a garage. When I jump it with my '97 OBW it starts right up. I drove it today thinking I would charge up the battery (going 85 on the curved entrance ramp onto I-75 is fun). When I got home the car started right back up, this was about 3:00 pm. Tonight about 8:30 pm the car wouldn't even turn over. The battery in an Interstate brand that was put on new in July of 2003 so it shouldn't be the battery. I'm guessing it might be the alternator. it has 153k miles on her and i don't know how old the existing alternator is? any suggestions?

Tdog