Current-sense amplifiers can monitor battery or solar cell currents, and are useful to estimate power capacity and remaining life. However, if the battery or solar source is a single cell, it’s difficult to find a low voltage solution that works below 1V and draws just microamps. A new class of nanopower analog ICs, namely Touchstone Semiconductor’s TS1001 0.8V/0.6µA op amp, makes a sub-1V supply current sense amplifier possible. With its extremely low power, the circuit can simply remain “always on”, providing a continuously monitored, averaged indication of current which can be read by a microcontroller without too much current drain.