Even though the red light is on, make sure the battery is completely inserted into the charger. When the battery is placed correctly into the charger you will hear it "click" into place.
The battery should be charged for a minimum of three (3) hours. This will provide a usable charge. To charge the battery completely leave the battery in the charger for six (6) hours. The battery can not be overcharged and can stay in the charger indefinitely. The approximate run time for the Scum Buster is 30 minutes. Your run time may vary based on the age of your battery as well as your application.