Hydrogen sulfide and sulfur dioxide evolution from a valve-regulated lead-acid battery

Two incidents concerning copper contamination associated with uninterruptible power systems (UPS) were observed. Valve regulated lead-acid (VRLA) batteries used in the UPSs for back-up powering were diagnosed as the possible source of the contamination. One of the VRLA batteries from the damaged UPS unit was subjected to overcharge in the laboratory, to simulate the incident. Overcharge currents greater than 10 amperes, coupled with battery temperatures over 60°C, can cause a VRLA battery to release significant amounts of hydrogen sulfide and sulfur dioxide. Under extreme conditions, hazardous levels of hydrogen sulfide could be generated. The authors conclude that the contamination was due to copper sulfide, Cu₂S, and copper oxide, Cu₂ O, formed on copper surfaces as a consequence of hydrogen sulfide evolution and the high humidity inside the UPS enclosure resulting from battery venting