The batteries go in the battery compartment, which is located on the back of the Swiffer Wet Jet. The battery compartment has a cover that needs to be removed to access them. The cover is usually marked with a symbol that indicates where the batteries go. Once the cover is removed, insert the batteries into the compartment according to the polarity markings inside. After the batteries are inserted, replace the cover and make sure that it is secure before using the Swiffer Wet Jet.