Hi Melissa,
It will be a 'labor of love', this nurturing of the Bad Boy into the Good Boy.... :-)
I don't know anything about the Bad Boy line,, but have a 48V 4X4 electric Polaris Ranger and the basic malfunctions may be similar. As already noted, if the error lights on the charger are indicating "no battery", then it would be worth (a) finding the main + and - terminals of the battery pack as a whole (I'm assuming lead acid batteries, 12V arrayed to deliver 48V) and disconnecting them first for inspection, but also because it makes it a bit safer (?) to inspect the terminals of the other batteries in the bank. The cables running from the charger to the main battery posts can be checked with a multimeter set for 'continuity' although I'm not sure how sensitively this will detect anything but a complete break in the wire. Now (b) although laborious, if the vehicle has sat for a while uncharged and unused, it will be important to check each battery for both charging ability (12V charger if these are indeed that voltage) and load tolerance using a load tester. A battery can exhibit 12V status, but not pass a load test and will not appreciably contribute to the bank. If either through battery replacement or passing the test and reassembling using cleaned and/or new connection cables, now see if the bank will accept charge from the charger. If not, then use word-of-mouth to find a 48V charger through golf cart contacts locally....use *that* charger attached however possible to the main battery charging posts in the bank. If your batteries are good, that should work....and if so, there is something wonky with the onboard charger and/or its connections. If that's the case, you will be deciding on whether or not to replace that stock charger or just go with the many offerings out there of 48V golf cart chargers. However....
If I'm not mistaken, Wheaton Labs has many skilled inhabitants in solar power and solar battery charging and I would encourage you to look into integrating a solar charging station with the perhaps not-so-Bad Boy. Additionally, if there are bold LiFePO4 battery aficionados there locally, there are several kits out there for replacing legacy battery banks with newer LiFePO4 batteries....you will find these for Bad Boy as well.f
For additional hopefully helpful info, try
https://www.facebook.com/groups/606703396197242/buy_sell_discussion if you are a Facebooker and also look for Bad Boy Buggy troubleshooting in the 'Cartaholics' and 'Buggies Gone Wild' golf cart forums online. Good luck.....Let's hope we see a healthy Good Boy again at WL!
Edit: If you can get an accurate Model-Year of this Bad Boy, there is often much tucked away on the internet in the way of owner's and shop manual as well as wiring and assembly diagrams.