It is imperative to determine accurately battery discharge characteristics at various battery operating temperatures, which vary significantly over the vehicle lifetime and which strongly impact the performance, driving range and durability of batteries used in electric vehicles. In this study, an experimental facility has been developed to measure the battery discharge characteristics accurately through precise control of operating temperatures utilizing a water–ethylene glycol solution in a constant temperature thermal bath. The results show a maximum variation of 0.3 °C temporally and 0.4 °C spatially in battery temperature throughout the discharge tests at a 3C discharge rate, in contrast to 13.1 °C temperature change temporally and 4.3 °C spatially when using the conventional air convection temperature control method under the same test conditions. The new method of battery temperature control developed in this study yields more accurate battery discharge characterization due to both the elimination of state-of-charge drift caused by spatial variations in battery temperature, and inaccurate discharge characteristics due to battery heat up at various discharge and ambient conditions.