A battery system , comprising: a thermally conductive base member ; a thermal interface member disposed on a surface of the thermally conductive base member , the thermal interface member having first and second arcuate-shaped surfaces and a first groove , the first groove being disposed between the first and second arcuate-shaped surfaces and extending into the thermal interface member ; a battery module having a first pouch-type battery cell , the first pouch-type battery cell having a first outer housing with a first end portion and a second end portion , the first end portion of the first outer housing having a first extension portion and first and second arcuate-shaped end surfaces , the first extension portion of the first outer housing having a first end and a second end , the first arcuate-shaped end surface of the first outer housing extending from the first end of the first extension portion of the first outer housing , the second arcuate-shaped end surface of the first outer housing extending from the first end of the first extension portion of the first outer housing and away from the first arcuate-shaped end surface of the first outer housing ; and the first pouch-type battery cell being disposed directly on the thermal interface member such that the first extension portion of the first pouch-type battery cell is disposed in the first groove of the thermal interface member , and the first extension portion of the first outer housing directly contacts the thermal interface member , and the first and second arcuate-shaped end surfaces of the first pouch-type battery cell are disposed directly on and against the first and second arcuate-shaped surfaces , respectively, of the thermal interface member . a thermally conductive base member ; a thermal interface member disposed on a surface of the thermally conductive base member , the thermal interface member having first and second arcuate-shaped surfaces and a first groove , the first groove being disposed between the first and second arcuate-shaped surfaces and extending into the thermal interface member ; a battery module having a first pouch-type battery cell , the first pouch-type battery cell having a first outer housing with a first end portion and a second end portion , the first end portion of the first outer housing having a first extension portion and first and second arcuate-shaped end surfaces , the first extension portion of the first outer housing having a first end and a second end , the first arcuate-shaped end surface of the first outer housing extending from the first end of the first extension portion of the first outer housing , the second arcuate-shaped end surface of the first outer housing extending from the first end of the first extension portion of the first outer housing and away from the first arcuate-shaped end surface of the first outer housing ; and the first pouch-type battery cell being disposed directly on the thermal interface member such that the first extension portion of the first pouch-type battery cell is disposed in the first groove of the thermal interface member , and the first extension portion of the first outer housing directly contacts the thermal interface member , and the first and second arcuate-shaped end surfaces of the first pouch-type battery cell are disposed directly on and against the first and second arcuate-shaped surfaces , respectively, of the thermal interface member . <EOS>