A battery-powered system comprising: 1) a housing adapted to contain electro-mechanical machines; and 2) an apparatus disposed within the housing. The apparatus comprises: i) a battery configured as an annular cylinder having an inner diameter, an outer diameter, and a length; and ii) a cylindrical device disposed within a cavity formed by the annular cylinder of the battery. An outer diameter of the cylindrical device is substantially the same as the inner diameter of the battery and the cylindrical device has a length substantially equal to the length of the battery. The cylindrical device may be a fluid reservoir or a second battery.