This paper discusses miniaturized Pb/HBF4/PbO2 reserve batteries (MRB) for military applications as in-flight power sources for small-caliber electronic fuzes, where the setback acceleration and high-spin force in firing environments are used to activate the MRB. The MRB is composed of a series configured 23 bipolar electrodes, an isolated glass ampoule filled with an electrolyte and an internal cutter for breaking the glass ampoule. The MRB is designed to furnish high-voltage electrical energy with a fast activation time in gunfire environments and must have a 20-year shelf life. The electrolyte volume is determined from the simulation results of a CFD program (FLUENT) for reduction in design time and cost. Two kinds of MRBs have been designed and fabricated: MRB-S with one narrow electrolyte-filling microchannel and MRB-D with two. In the experimental study, spin tests under 10,000× g's and ∼20,000rpm conditions and a fire test under 43,000× g's and 57,000rpm conditions have been made. The fabricated MRB with a diameter of 16mm and a height of 13mm has achieved a maximum voltage of 34.6±0.4V, an activation time of 8.6±0.6ms and a maximum capacity of 37.4±0.4Ws at an optimized electrolyte volume of 180mm3. The test results have verified that the activation time of the MRB at a low temperature of −32°C can be improved by decreasing the flow resistance of the electrolyte in spite of the decreased ion mobility.