Abstract: A voltage level monitoring and indicating apparatus (10) including a voltage-to-frequency converter (12), an input conditioning circuit (16) that shifts voltage signals received from different voltage sources to the same input level for the converter (12) which then produces a proportional output frequency signal, a microprocessor (40) which is software programmed to produce voltage level data in response to the output frequency signal from converter (12), and a display (42) which displays a range of numbers in response to the voltage level data. Prior apparatus are not state-of-the-art microprocessor based and require different designs when coupled to different voltage sources. The present invention is microprocessor based and has the same input conditioning circuit that can be coupled to different voltage sources for use principally to indicate voltage levels of batteries on electric fork lift trucks.