Electromotive Force Based State of Charge Estimation for Primary Battery Powered Devices

Due to its low cost, primary battery such as alkaline battery and carbon battery is still one of the main options for powering low power devices, such as wireless sensor nodes. In order to prolong the survival time, it is necessary to accurately estimate the State of Charge (SOC) of the battery and then dynamically adjust the working modes of device. Among the existing SOC estimation methods, Electromotive Force (EMF) is generally recognized as an accurate indicator. Taking popular alkaline and carbon batteries as examples, this paper studies the relationship of EMF and SOC through intermittent discharge experiments with both constant current and constant resistance loads. Experimental results show that the change patterns of SOC with EMF are very similar for batteries with the same chemical material. Meanwhile, the discharge mode (constant current or constant resistance) and load have very little effect on the relationship of EMF and SOC. Then, the SOC estimation models based on EMF are established using different fitting methods. Verification results show that, for the target primary batteries, the piecewise linear fitting method is the most accurate, and its estimation error is no more than 1.4%.