Assessment of lead-acid battery state of charge by monitoring float charging current

In 1988, one user of flooded Pb-acid secondary batteries in a nuclear power plant began to measure float current in addition to specific gravity readings. A total of 780 cells were monitored. The results of this experience are summarized in this paper. A review of some of the electrochemistry involved is also presented. The analysis of the collected data has led to the conclusion that float current monitoring is preferred over specific gravity readings for assessing the state of charge of a Pb-acid battery. Now the problem turns to the availability of cost-effective, accurate provisions for measuring float current. The last part of this paper presents a test instrument design specifically for taking float current readings