A simple, global model for the optimal combination of ultracapacitor and battery for electrical energy storage is developed. The goal for this hybrid storage technology is to reduce the system life-cycle cost by making use of an ultracapacitor's claimed long cycling-life in order to supplement relatively cheap, but cycle-limited battery storage. The model is built up of two independent sub-models that allow flexibility in the relative proportion of system energy storage. An analysis performed in this paper indicates that ultracapacitor/battery storage systems may be cost effective for high-cycle applications. (c) 2008 Elsevier B.V. All rights reserved.