This paper describes electrochemical behavior of microscopic batteries based on both the lithium/ion and Ni/Zn couples. These batteries are being developed for use in MEMS devices and other microelectronics, especially remote, autonomous sensors. Many of these applications require a combination of long cycle life, moderate energy storage capability, and periodic high power output. Batteries have been made using high-volume, lowcost, fabrication techniques, described in prior publications. These batteries have been built and evaluated for their electrochemical performance. Power output from both types of cells is impressive; current densities of 80 - 100 and 20 - 50 mA/cm2 have been observed, for discharges of several seconds, for Ni/Zn and Li/Ion cells, respectively. Much higher current densities are observed for discharges lasting a few milliseconds, such as would be needed in many applications. Specific capacities of 2 - 4 C/cm2 are also obtained. These and other electrochemical behaviors will be discussed.