Counterflow heat exchanger with side entry fittings

A battery cell heat exchanger having a pair of plates that together define a fluid passage having a first channel permitting fluid flow from a first end of the plate pair towards a second end of the plate pair, and a second channel permitting fluid flow from the second end towards the first end of the plate pair. The plate pair together defining a first conduit at the first end of the plate pair, the first conduit being in fluid communication with the first channel. One of the pair of plates having an aperture permitting fluid flow from the second channel to a duct, the duct coupled to the one of the pair of plates having the aperture and having a second conduit in fluid communication with the aperture; where the first conduit and the second conduit lie in the plane defined by the pair of plates.