A battery system includes a battery module that utilizes the first and second retention housings to hold a battery cell retention frame therein that can be either air cooled or fluid cooled. In particular, the first and second retention housings have an inlet port and an outlet port, respectively, for routing fluid through the battery cell retention frame for cooling cylindrical battery cells thereon. Alternately, the battery cell retention frame can be air cooled for cooling the cylindrical battery cells. Also, the first and second retention housings provide improved structural integrity to the battery module.