Capacity monitoring in advanced battery chemistries

Monitoring the battery capacity of advanced battery chemistries such as the new Ni-MH and lithium ion cells poses many unique design problems. With the terminal voltage varying greatly with discharge rate and temperature, and charge acceptance complicating the partial charge estimates, capacity monitoring methods become critical for accuracy and simplicity. To enhance accuracy, both the capacity reference and available capacity monitor must be periodically recalibrated to account for the effects of battery wear-out, different charge/discharge conditions, and multiple partial cycles which allow small estimation errors to accumulate. Cost, accuracy, circuit size, and operating current are all critical design parameters when implementing a capacity monitoring circuit for new battery chemistries. The authors discuss these points