The 2 most likely culprits are the battery or the regulator.
How old is the battery and what type? If it's the original Banner they only last 2 or 3 years
Battery voltage needs to be checked under load so switch the dashboard display to volts and try to start the car. The voltage shouldn't go any lower than 10 and a bit volts, if it does you need a new battery
If the battery is OK and charges up then the regulator has probably gone. Start the car and the voltage at 2,000 or more revs should be about 14.4 volts. If not then change the regulator, ideally for a Harley type as per the Alternative parts list.
