State-of-charge estimation for lead-acid batteries based on dynamic open-circuit voltage

The charging and discharging characteristics of lead-acid batteries are investigated to learn the relationship between the state-of-charge (SOC) and the dynamically changed open-circuit voltage. Experimental results indicate that the open-circuit voltage of the lead-acid battery varies methodically with the charging or discharging rates and the duration since they have been disconnected from the load or charger. Accordingly, a dynamic open-circuit voltage method by taking account of the open-circuit time and the previous charging/discharging rate is capable of more precisely estimating the SOC in a shorter time. Experiments that emulate practical operations are carried out to demonstrate the effectiveness and accuracy of the proposed method.