Gas evolution, dryout, and lifetime of VRLA cells an attempt to clarify fifteen years of confusion and misunderstanding

This paper compares a reasonable sample of the more than 15 years published data on valve-regulated lead-acid (VRLA) batteries in a single standardized fashion. Using the standardized criterion of ml of hydrogen per day per 100AH and calculated time to 10% water loss (which the authors have previously reported is equivalent to capacity loss below 80% of rated value), they find: times to 10% water loss ranging overall from 6 to 1300 years from literature data on laboratory and field studies of positive grid corrosion, cell weight loss and actual quantities of gas collected for both AGM and GEL cells; laboratory corrosion data generally predict the longest times to 10% water loss (30-100 years), while positive grid corrosion in actual VRLA cells generally predict less than 10 years; and direct gas collection results tend to predict greater lifetimes than field corrosion data, but are contradicted by the shorter lives predicted from weight loss measurements. The requirements of various national and international VRLA standards are also compared in this standardized fashion. The extraordinary range and disparity of literature results, made obvious by the use of this standardized approach, suggests its more widespread application might be helpful in developing a clearer understanding of the mechanisms which govern VRLA performance, life and failure modes.