The battery indicator is your charging light, wired to the alternator it tells you if 12v are being dispatched to the battery. The light stays on when the regulator pack gives up, so its fair to say you are shopping for a alternator. My advice is to replace the battery at the same time and then you have peace of mind.
www.williamsdiesels.com if you need any further help, my number is on there
Deano
September 2008