The LT 1239 is a micropower backup battery management system for portable computers and instrumentation. It contains two regulators for regulating the battery voltage and memory voltage and a comparator for switching between main power and backup power. The first regulator provides a constant voltage charge for the backup batteries and is adjustable from 3.75V up to 20V. An equalization amplifier combined with the first regulator provides precision charge equalization for a 2-cell lithium-ion system. A second regulator with 4.85V output provides a regulated backup battery voltage to the memory when main power is lost. The second regulator also isolates the backup battery from the main 5V supply during normal operation when the memory is being powered by the 5V supply.