Check to see if charging plug is receiving power. The charge plug should be connected somewhere so that it receives full time power. Verify voltage with voltmeter.
If your light bar is equipped with a charging light, plug your light bar into the charger and verify that the charging light is lit.
Check to see if battery leads have come off of the battery terminals.
If the charger is a cigarette lighter charger, plug the charger into the power port but not into the light bar. The red LED on the charger should be lit if there is power to the port. If the LED does not light, unscrew the end of the cigarette lighter charge plug and check the 5 amp fuse; replace if it has been blown.