The MAX17040/MAX17041 are ultra-compact, low-cost, host-side fuel-gauge systems for lithium-ion (Li+) batteries in handheld and portable equipment. The MAX17040 is configured to operate with a single lithium cell and the MAX17041 is configured for a dual-cell 2S pack. The MAX17040/MAX17041 use a sophisticated Li+ battery-modeling scheme, called ModelGauge™ to track the battery’s relative state-of-charge (SOC) continuously over a widely varying charge/discharge profile. Unlike traditional fuel gauges, the ModelGauge algorithm eliminates the need for battery relearn cycles and an external current-sense resistor. Temperature compensation is possible in the application with minimal interaction between a µC and the device. A quick-start mode provides a good initial estimate of the battery’s SOC. This feature allows the IC to be located on system side, reducing cost and supply chain constraints on the battery. Measurement and estimated capacity data sets are accessed through an I2C interface. The MAX17040/MAX17041 are available in either a 0.4mm pitch 9-bump UCSP™ or 2mm x 3mm, 8-pin TDFN lead-free package.