Grid-connected electrical storage has a high potential to support the transition toward a reliable decentralized and renewable energy supply. It is expected that lithium-ion batteries will play a major role in this transition, because of their high energy density and of the potential capacity that is offered by plug-in ( hybrid) electric vehicles. The use of lithium-ion batteries in grid support may result in additional degradation. Intelligent control of these batteries can assure that the additional degradation rate is minimized and their utilization is cost-effective. It is, therefore, imperative that the intelligent control has an excellent understanding of the aging behavior of the battery, therefore, it can maximize the benefits for the battery owner. Based on this logic, cycle life experiments were performed on lithium polymer cells in which the cell life dependence on the depth of discharge was investigated. Other cell characteristics that were studied include the equivalent series resistance and the efficiency.