Abstract: In one embodiment, the present invention provides a method for forming battery tray for holding cylindrical cell batteries. The method includes forming a battery try including a base support having a generally flat bottom surface and multiple adjacent cylindrical cavities are formed within the base support, using a circle packing algorithm to form the cylindrical cavities. The adjacent cavities each have at least some interstitial cylindrical riser wall structures formed with a predetermined height to hold the cylindrical cell batteries. In another embodiment, the present invention allows for packing maximum energy density per layer. This allows lifetime and power output of a battery powered device to be optimized and/or increased.