The Helix Mobile Stairlift is designed to transport riders downstairs safely and efficiently. The lightweight and portable Mobile Stairlift Helix does not require pre-installed tracks and is able to carry up to 400lbs. This unit was designed for curved staircases, and the powered tracks can move independently of each other, offering a controlled lift up or down any staircase. This is an additional battery to go with your Helix Mobile Stairlift.