A novel Li-ion polymer battery (Li-IonPB) based on LiNi0.8Co0.2O2 as a cathode and an alternative composite anode (CA) is proposed for future application in hybrid electric vehicles (HEV). A micro-Li-ion polymer cell is prepared in situ inside the differential scanning calorimetry (DSC) sample pan, and the exothermic heat development is compared with that of the micro-lithium-solid polymer electrolyte cell. The thermal decomposition of both cells is further investigated from a qualitative point of view.