Electric vehicles and hybrid-electric vehicles generally have high-voltage batteries which are significantly larger than that of conventional internal combustion engine vehicles.  The smaller batteries of internal combustion engine vehicles are commonly 12 to 14 volts to power the ignition system of a vehicle's engine as well as other low voltage electrical accessories.  High-voltage traction batteries tend to be more susceptible to temperature rises during operation including electrical charging and discharging. 
In passenger vehicles, the traction battery is commonly enclosed within a compartment of the vehicle.  Typical compartments are not generally included in a climate controlled region within the vehicle.  The temperature of such a compartment may be elevated by heat emitted from the battery, or by the external environment.  Battery cooling efficiency may be reduced because airflow directed to the battery often undergoes a temperature increase prior to arriving at the battery due to the heat in the compartment in which it is enclosed.