94 Regal electrical problem

Hi folks… I own a 94 buick regal (runs great, til now). last week I got up early turned ignition wouldn’t start. Got a jump start and all was good. After work. same thing. Rinse and repeat every day. When I get a jump start and am driving my battery gauge on dash shows a staedy 15 to 18 (so I assume its not alternator). If I stop the vehicle and restart it, no problem. It seems the battery loses its charge after an extended period of time. Is there any OTHER reason than a bad battery that would cause this to happen… Many thanks