Methods and devices for attaching a battery to a helmet and attaching a battery to an additional device are disclosed. A battery may be mounted to the rear center of a helmet. Attaching and detaching a battery to and from a helmet may be performed with a tool or by hand. The battery may be used to power multiple devices through separate contacts, and a device may be attached to the battery while the battery mounted to a helmet. The battery also may be detached from the helmet and serve as a portable energy source.