The pump in style advanced battery pack uses 8 aa alkaline or rechargeable batteries. The black microfiber carrying case fits inside your breast pump bag, or can be attached to the bag strap for easy transportation. Provides up to 3 hours of pumping time. For use with all 9v Medela pump in style advanced breast pumps (manufactured January 2008 and after).authentic Medela spare parts are engineered, tested and approved to work specifically with your Medela breast pump. Non Medela spare parts can vary significantly in design, materials, and workmanship; all of which may affect the performance of your Medela breast pump.