Battery State of Charge (SOC) constraints are set to prevent the battery in Hybrid Electric Vehicles (HEV) from over-charging or over-discharging. These constraints have important consequences concerning battery lifetime and the fuel economy achieved by HEV power-split control systems. This paper presents results on how the Battery State of Charge (SOC) constraints effects Lithium ion battery aging and fuel economy when using the Equivalent Consumption Minimization Strategy (ECMS). The vehicle studied is a Honda Civic Hybrid. The battery used is A123 Systems’ ANR26650 battery cell. Vehicle simulation utilizes multiple combinations of highway and city drive cycles. For each combination of drive cycles, five SOC constraint ranges are used. Battery aging is evaluated using a semi-empirical model combined with the accumulated Ah-throughput method which uses, as an input, the battery SOC trajectory from the vehicle simulations. The tradeoff between fuel economy and battery aging is explicitly displayed for different combination of drive cycles and SOC constraints. The simulation results provide insight into how SOC constraints effect fuel economy as well as battery aging.