Sounds more like alternator. But, the only way to find out for sure is have them both tested. Honestly both could be bad - if the alternator is weak the battery has been taking up the slack. FWIW, Optima batteries don't live up to their hype or price tag anyway. Have it tested, replace if necessary (my hunch says 'yes') and go from there.
2001 GT Convertible
8 cylinders, 5 gears, red.
6 cylinders, 3 gears, also red.
Remember my motto kids: Be bitter, stay angry and blame everyone. It's on my fridge magnet!