You should have a tail light or rear bike light like the following which comes with a USB adaptor for recharging the Lithium polymer battery. It has two types of mount so that you can decide if you would like to locate it at the saddle or seat post.
You will also require a headlight or front bike light.
There are models that also come with helmet mount. What is the point of mounting your headlight on your helmet? Without moving your bicycle, you can shine the light in the direction you are looking at.
