A heat exchanger for thermal management of a battery unit having a plurality of battery cell containers each housing one or more battery cells, comprising: a main body portion having opposed ends and defining at least one primary heat transfer surface for surface-to-surface contact with a corresponding surface of at least one of said battery cell containers; a plurality of first fluid flow passages formed within said main body portion, each of said first fluid flow passages having a first end for inletting a fluid into said first fluid flow passages and a second end for discharging said fluid from said first fluid flow passages, said first and second ends (46, 48) defining a flow direction through said first fluid flow passages; a plurality of second fluid flow passages formed within said main body portion, each of said second fluid flow passages having a first end for inletting said fluid into said second fluid flow passages and a second end for discharging said fluid from said second fluid flow passages, said first and second ends (50, 52) defining a flow direction through said second fluid flow passages; an inlet manifold in fluid communication with said first ends of said first fluid flow passages; and an outlet manifold in fluid communication with said second ends of said second fluid flow passages; wherein said first and second fluid flow passages (40, 42) are arranged so as to alternate through said main body portion and wherein the flow direction of said first fluid flow passages is opposite to the flow direction of said second fluid flow passages; characterized in that said first and second fluid flow passages (40, 42) are formed by U-shaped flow channels having a pair of elongate fluid branches that are interconnected at one end by a turn portion such that said second ends of said first fluid flow passages are in fluid communication with said first ends of said second fluid flow passages; and wherein said inlet and outlet manifolds (54, 56) are arranged adjacent to each other at one end of the main body portion of the heat exchanger, one of said inlet and outlet manifolds (54, 56) being inwardly disposed with respect to the other one of said inlet and outlet manifold (54, 56) and offset with respect thereto. a main body portion having opposed ends and defining at least one primary heat transfer surface for surface-to-surface contact with a corresponding surface of at least one of said battery cell containers; a plurality of first fluid flow passages formed within said main body portion, each of said first fluid flow passages having a first end for inletting a fluid into said first fluid flow passages and a second end for discharging said fluid from said first fluid flow passages, said first and second ends (46, 48) defining a flow direction through said first fluid flow passages; a plurality of second fluid flow passages formed within said main body portion, each of said second fluid flow passages having a first end for inletting said fluid into said second fluid flow passages and a second end for discharging said fluid from said second fluid flow passages, said first and second ends (50, 52) defining a flow direction through said second fluid flow passages; an inlet manifold in fluid communication with said first ends of said first fluid flow passages; and an outlet manifold in fluid communication with said second ends of said second fluid flow passages; wherein said first and second fluid flow passages (40, 42) are arranged so as to alternate through said main body portion and wherein the flow direction of said first fluid flow passages is opposite to the flow direction of said second fluid flow passages; characterized in that said first and second fluid flow passages (40, 42) are formed by U-shaped flow channels having a pair of elongate fluid branches that are interconnected at one end by a turn portion such that said second ends of said first fluid flow passages are in fluid communication with said first ends of said second fluid flow passages; and wherein said inlet and outlet manifolds (54, 56) are arranged adjacent to each other at one end of the main body portion of the heat exchanger, one of said inlet and outlet manifolds (54, 56) being inwardly disposed with respect to the other one of said inlet and outlet manifold (54, 56) and offset with respect thereto.