This paper investigates the impact of battery cooling ancillary losses on fuel economy, and optimal control strategy for a series hybrid electric truck with consideration of cooling losses. Battery thermal model and its refrigeration-based cooling system are integrated into vehicle model, and the parasitic power consumption from cooling auxiliaries is considered in power management problem. Two supervisory control strategies are compared. First, a rule-based control strategy is coupled with a thermal management strategy; it controls power system and cooling system separately. The second is optimal control strategy developed using Dynamic Programming; it optimizes power flow with consideration of both propulsion and cooling requirement. The result shows that battery cooling consumption could cause fuel economy loss as high as 5%. When dynamic programming coordinates control of the powertrain and the cooling system in an optimal way, the fuel consumption penalty due to cooling losses is reduced to 3.7%, and battery duty cycle becomes milder. Finally, rules are extracted from the optimal strategy, and a refined rule-based strategy is presented.