Battery has sulfur smell

Why does my battery have a sulfur smell?

Stop charging. The sulfur smell comes from the formation of hydrogen sulfide when the unit is at full voltage, but the charger continues to flow full current as opposed to going into float mode. Check the battery voltage meter and confirm that there is a full charge. Check inverter/charger setting are correct for this unit (20a, 40a, 55a, etc.). Check to make sure the dip switches are correct (1000, 1800, 2055 models- you may need to remove piece).