The battery pack for pump in style advanced uses 8 AA alkaline or rechargeable batteries. Provides up to 1 hour 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. <p> Pump in Style comes in two types in terms of input voltage, 9V and 12V. You can identify its voltage by looking at the faceplate of your pump. This battery pack is designed to be used with the "9VDC" pump. If you have a 12VDC pump, DO NOT buy from this listing. </p> <p> Authentic Maymom spare parts are engineered, tested and approved to work specifically with the intended breast pumps. Satisfaction guaranteed or your money back. </p>