Modern Buddy

Howdy, I have a Buddy 125. Just bought a new battery because the existing one wouldn't hold a charge. New one won't hold a charge either so I'm thinking there is another issue. Here's what I know that may be related: 1) My low beam head lamp quit operating; don't know if it is all related or simply coincidental. 2) The scooter will start when the battery charger is connected. 3) When I started it there was a loud noise;may have been a back fire? 4) I put Stabl in the gas so I don't think the gas is bad . . . and I only use ethanol-free gas. 5) Fuse looks good. Any suggestions? Does it sound like the spark plug? What would make the scooter battery not hold a charge, even w/ a new battery? I appreciate suggestions! Thanks.

Start the scooter and put a voltmeter on the battery terminals to see if the alternator is working correctly. Also check across the battery when shut off to see if something is draining the battery overnight. It could be that the voltage regulator is faulty or that there is a parasitic load on the battery when the key is off.