Battery

The battery is just something to hold the power. It has to be rechargable (Obviously) and I would personally recommend for it to hold a lot power, becuase you don't want to continue walking, and waste those valuable steps on a full battery! Also the battery doesn't really have to be a battery, you can just plug it into anything that takes in charge. You could plug it into your phone, or your laptop (I mean if you want to walk around with your laptop, thats fine) or anything that has a USB on one side.