This disclosure describes various embodiments of a battery assembly for an electrified vehicle battery pack. The battery assemblies include one or more battery cells (e.g., cylindrical, prismatic, or pouch cells) and a cooling device extending at least partially through the battery cells. The cooling device is configured to either conductively or convectively cool the battery cells. In some embodiments, the cooling device is a solid rod, a hollow tube, a slab, or some combination of these features. In other embodiments, the cooling device connects to a coolant manifold configured to communicate coolant for convectively cooling the battery cells of the battery assembly.