In order to make reasonable use of the electric energy of the thermal battery,the trajectory of thermal battery activated in the sky is considered.The thermal battery technical characteristics,working principle and activation methods are introduced.The research background is the thermal battery on short time,medium time and long time.The size and weight of the thermal battery under two different activation modes including ground activation and sky activation were analyzed and calculated.The results show that sky activation of the thermal battery can greatly reduce the size and weight which satisfy the goal of miniaturization and lightening of thermal battery better.