Green light stays on 14.4v black and decker charger

SOURCE: 14.4V Drill Battery Will not Charge

The battery is 14.4 volts so the charger should be 14.4 volts.

SOURCE: batteries don't charge

Dust getting in the charger is a problem, Try blowing it out with a moisture-free dust remover, found at most any store. Green flashing means improper power, due to dust or power from the outlet, try a differant wall outlet. Red flashing means the charger or battery is to hot and must cool down before it will charge. The charger will not charge a battery if the lights are flashing. Solid Red light means it is charging and solid green light means it is charged. Plug the charger in first before putting the battery on the charger. If the charger has been droped or hit the floor the coil inside could have broke loose and dammaged the charger requiring it to be replaced.

SOURCE: dc1804f charger

If you have tried discharging the batteries prior to charging them already with no result and from what you describe in your post, then I would have to say the charger has issues. Go to HD or Lowes (not sure if Lowes carry Makita) but another charger and test your battery again. If you get the same fault, there is an issue other than the charger, if not you need a new charger anyway. If you get the same fault with the new charger, you can always return the new one. Short of opening up the charger and using a volt meter, this is the easiest way to test to pinpoint the real problem. I hope this helps and good luck!

SOURCE: Brand new Makita DC18RA charger wont charge the batteries.

Return to store for replacement.

SOURCE: Makita 18v lithium battery when put on charge

This isn't true because I have a second charger and it works fine