A digital current capacity tester for rechargeable batteries was described. The capacity tester was built by researchers at NIOSH and was designed to test the types of battery packs commonly used in equipment used for industrial hygiene field studies. It could measure current capacities of up to four individual battery packs simultaneously. The tester was housed in an aluminum cabinet with a hinged front panel. Four sets of input jacks and push buttons were attached to one side of the cabinet. Four printed circuit boards, each an independent battery tester, were attached to the front panel. A liquid crystal display (LCD), a light emitting diode (LED), and a pair of slide switches were attached to each printed circuit board. The LCD provided a milliampere hours readout of the test results and the LED indicated that a battery test was in progress. One of the slide switches permitted the user to select an appropriate constant current discharge rate. The other switch was positioned according to the number of the cells in the tested battery and established the cutoff voltage at which discharge was to be discontinued. The tester was designed originally for testing nickel/cadmium battery packs; however, it could be modified easily to test any rechargeable battery. The authors conclude that because the battery capacity tester gives a true indication of the energy available from a nickel/cadmium battery, the tester allows any battery powered instrument to be used with greater confidence. Directions for calibrating and using the tester were given, and a circuit diagram and parts list were provided.