The battery pack uses 8 AA alkaline or rechargeable batteries. Provides up to 3 hours of pumping time. Please note using battery pack might not have the same suction power as using the AC adapter because battery will drain down as it is used. Adjust the power setting on the pump to fit your comfort or replace old batteries with new batteries. Please use rechargeable batteries for better performance. <p> </p> <p> Authentic Maymom spare parts are engineered, tested and approved to work specifically with the intended breast pumps. Satisfaction is guaranteed or your money back. </p> <p> Hygeia is a registered trademark of Hygeia. Maymom is not affiliated with Hygeia. Hygeia does not endorse this product. </p>