Most research and development in the field of electrochemical energy storage (i.e. batteries and capacitors) is directed at increasing energy density. Such advancements enable longer range, increased run times, and improve cost in critical applications such as electric vehicles and consumer electronics. There is, however, a need to improve life and durability characteristics of energy storage in high duty cycle applications such as stop-start vehicles, regenerative braking in HEVs, and many grid and industrial applications. Currently, rechargeable batteries meet the energy requirements of these high duty cycle applications but lack in durability and low temperature power performance. Ultracapacitors (also called supercapacitors or electrochemical capacitors), are able to meet durability and low temperature requirements but fall short with cost and energy density. Ionix has developed a unique hybrid design that allows the energy of batteries to be combined with the durability and electrical performance of capacitors to create a device that meets the demands of high duty cycle applications such as stop-start vehicles, regenerative braking in HEVs, and many grid and industrial applications.