If its the right charger, and connected correctly, then it is probably just time to replace the battery. Try checking out http://www.batteryinternational.com/flashlight-batteries-streamlite---maglite.html for a replacement flashlight battery. Also, I'm not sure exactly what you mean by saying the charger is putting out 13.7 volts, but make sure you aren't using a charger that is too powerful, that can destroy the battery. Check out http://www.batteryinternational.com/battery-chargers-6-volt-battery-chargers.html. You shouldn't use a charger any larger than that. Hope that helps