Wow, I haven't been here for a year.

I'm having the exact same problem. Had the alternator checked (Sears $10.95). It still works, but is not putting out enough amps. Now the battery is going bad as well. I think I overworked the alt over the last year by running my 700W stereo. I need a new one and am looking for a high output. Found a 135 amp for $200. If you run a high output stereo or other electronics, you may be having the same problem.