Lithium-ion batteries are currently being produced and used in large quantities in the automobile sector as a clean alternative to fossil fuels. The thermal behavior of the battery pack is a very important criterion, which is not only essential for safety but also has an equally important role in the capacity and life cycle of the batteries. The liquid battery thermal management system is a very efficient type of thermal management system, and mini-channel-based liquid cooling systems are one of the most popular type of the battery thermal management system and have been researched extensively. This paper mainly intends to study the effects of tapering, the addition of grooves to the channel, the use of different nanofluids, and the flow direction of coolant on the thermal performance of the battery pack using a three-dimensional computational fluid dynamics model. The results suggest that converging channels can be used to control the temperature rise, while diverging channels can be used to control the temperature deviation. The addition of grooves and the use of nanofluids were beneficial in reducing the temperature rise. The final setups were able to reduce the maximum temperature rise by 2.267 K with a substantial pressure drop increase and by 1.513 K with an increase in pressure drop of only 19.92%.