The LTC4150 measures battery depletion and charging in handheld PC and portable product applications. The device monitors current through an external sense resistor between the battery's positive terminal and the battery's load or charger. A voltage-to-frequency converter transforms the current sense voltage into a series of output pulses at the interrupt pin. These pulses correspond to a fixed quantity of charge flowing into or out of the battery. The part also indicates charge polarity as the battery is depleted or charged.