Unregulated temperature excursions in VRLA standby battery enclosures

Laboratory testing on valve regulated lead-acid (VRLA) batteries under conditions designed to accelerate failure lead to life predictions that are inconsistent with results seen in actual field applications. In most standby battery enclosures, units experience elevated temperatures and thermal cycling not encountered in laboratory experiments. This study includes a qualitative thermal model for such cabinet enclosures, and it is shown that batteries operate under conditions that do not accurately reflect the surrounding environment. In most cases, overheating of batteries leads to shortened life; in extreme cases systems can go into catastrophic thermal runaway, resulting in total system failure. Thermal runaway is defined in practical terms, and results of experimental studies are presented that point toward the source of this phenomenon.<>