Electric vehicles (EVs) and plug-in hybrid electric vehicles (PHEVs) are considered as a promising future solution for sustainable transportation. This is due to the reduction in energy consumption when compared to conventional internal combustion engine (ICE) based vehicles. EVs and PHEVs contain an Energy Storage Systems (ESS). This increases the complexity of the system but also provides additional margins and fields for optimization.One of the most important elements of these vehicles is the ESS. The electrochemistry nature of battery systems is inherently sensitive to the temperature shifts. The shifts are controlled by the thermal management system of the traction battery systems, for electric-drive vehicles, which directly affects the overall vehicle dynamics. These dynamics include performance, long-term durability, and cost of the battery systems. Hence, thermal management becomes an essential element in the achievement to meet the demand for better performance.A thermal management system utilizing liquid cooling achieves better performance over other common air-cooled methods. The next step in achieving optimized performance is utilizing an active thermal management system to optimize battery throughput. Optimization extends battery state of health (SOH) providing a direct correlation between increased performance, durability, and cost. Current technology utilizes a series coolant loop, which creates temperature disparities between modules.This paper discusses the features and control of an active liquid cooling system for a battery system comprised of Lithium Ion, Li-Ion, batteries. Comparing series and parallel coolant loops using electronically actuated valve technology. Parallel coolant loops provide an attractive means to reduce the temperature disparity in the different modules. Resulting in a temperature reduction of approximately two Kelvin under the same load and constraints.