The S1 boasts so many great features, including an inbuilt rechargeable battery and is designed to truly meet the needs of moms wanting to feel confident that they have an effective, powerful breast pump to support supply while also incorporating features to make life a little easier. Like all Spectra pumps, the S1 is a closed system - a physical barrier between the milk and the pump ensures hygiene and motor performance. The S1 is intended to rival the Medela Symphony, and even surpass it with some of its innovative features designed to make life easier for moms. The S1 is hospital grade - strong and efficient enough to support milk supply. Used in hospitals to establish a milk supply for moms with premise. With a maximum suction strength of 350mmHg and the ability to be used as a single or double pump, plus a host of additional features, the S1, like her sister the S2, is set to become the ultimate breast pump to support U.S. moms. Completely flexible, touch button with the S1 pump's digital controls. These allow you to set the pumping program to the speed and rhythm most effective for your body. The pump will start in 'massage mode', a short, shallow mode designed to stimulate your body's letdown reflex (start the milk flowing) just like how your baby tells your body to start milk flow. The pump will then switch to expression mode, a deeper, slower pattern of suction which mimics how your baby nurses when the milk is flowing. For women who find it hard to get a letdown when pumping, this feature really helps - switch back and forth as needed. The suction is also adjustable whether in let-down or expression mode. Includes a timer and nightlight. You can see on the picture that you can adjust both cycle (how often the pump 'sucks') and vacuum (the strength of the suction) easily, and the digital display allows you to see your program at a glance. Can be used with it's inbuilt battery for 1 hour on full charge or plug it in...it's up to you.