Most space missions utilize energy storage, such as a rechargeable battery onboard the spacecraft. Therefore, a continuing evolution of battery performance can benefit a wide gamut of space science missions conducted or planned by NASA and worldwide space agencies. Venus presents the most significant challenge to energy storage systems due to a combination of high temperature (465 °C) and the presence of corrosive gases (CO 2 , CO, SO 2 , and N 2 ). On a NASA-funded project, a high-temperature (465 °C) lithium−selenium (Li∥Se) battery consisting of an anode of molten Li, a lithium-ion conducting ceramic electrolyte (garnet-type Li 6.4 Al 0.2 La 3 Zr 2 O 12 , LLZO), and a cathode of Se have been conceptualized. The proof-of-concept Li∥Se cells were built using baseline cell electrodes, electrolytes, and cell design. The fabricated Li∥Se cell was tested in an in-house built cell holder placed in an argon-filled glovebox. Electrochemical testing includes time-dependent open-circuit voltage measurements across a wide temperature range (230−500 °C) and electrochemical cycling at multiple current rates at 465 °C. Further cell components and design optimization will enable higher current charge−discharge and a longer battery life span over a wide temperature range. In addition, the use of high-energy electrodes will encourage longduration and safe Venus surface exploration.