voltage regulator went on my Harley a month or so ago...same symptoms. If the your battery doesn't get re-charged consistantly, or if your battery is over working the alternator because it is faulty, both can cause this problem. Ruin a battery or ruin an alternator. Checking the voltage from the alternator to see if it is working is where I would start...you already replaced the belt and the battery, so that is all that is left. The battery needed replaced, and very well might be why your voltage regulator/alternator is shot. Good luck, I know you will figure it out.

And, the a slipping belt could cause all this to start with. Overworking the alternator, never really fully charging the battery. An old battery is harder for the alternator to charge to begin with....it all snow *****. I put in new batteries every couple of years in my daily driver, and a maintainer on the XF's...