FRAM Hybrid Battery Compartment Air Filters prevent airborne containments like road dust, dirt and pollen particles from entering your vehicle's battery compartment. The air inside your vehicle can be up to six times dirtier than the air outside. Replacing a clogged air filter can lead to improved air flow to your battery. Install this filter in your battery pack compartment located in the rear cargo area on the driver side. Replaces: Motorcraft FP-51, Premium Guard PC5571, PurolatorC25571, and WIX 24477.