Silicon Labs’ application note about a low power current measurement circuit using TS1001 nano power op-amp paired with low-power CY8C38 microcontroller, Link here (PDF)
Pairing a simple circuit using nanopower analog op amps with a microcontroller can monitor single battery cells and solar harvesters. Pairing up a 0.65 V/1 µA nanopower op amp with the low-power Cypress PSoC3 microcontroller and some simple external circuitry can yield a very low current measurement system, suitable for monitoring miniature power harvesting solar cells or a single-cell battery. The circuit operates on a few microamps at 1.8 V; optionally, the whole circuit can be self-powered from the source being measured. The op amps operate from voltages as low as 0.65 V and are connected directly to the cells; the PSoC3 microcontroller utilizes an internal boost regulator which operates from sources as low as 0.5 V.