An electronic fuel gauge accuracy study

Abstract

This paper is prepared for battery cell manufacturers who want to optimize battery pack fuel gauging in light of uncertain user patterns and less-than-ideal cell behavior outside of the laboratory. The idea of coulomb-counting the gain or loss of energy to and from the battery pack is a popular and low-cost method. This technique finds use in nickel-metal hydride (Ni-MH), nickel-cadmium (NiCd), sealed-lead acid (SLA) cells and lithium-ion (Li/sup +/) battery packs. It is critical for battery pack suppliers to understand how well electronic fuel gauges estimate the energy flow through the battery and correct for cell effects, such as, charge efficiency, available capacity and the cell's self-discharge. It is not apparent to a user that a cellular telephone will lose its capacity faster on a hot, summer day than on a freezing, winter day. This information becomes the basis for reporting the portable appliance's fuel tank level to its user. This paper reviews a new portable appliance-the two-way pager-that uses two 450 mAh cells for a power source.