What Sparked the Arizona Battery Fire? LG Chem Has a Different Version This is the second in a series of exploring the repercussions of the most prominent battery fire in recent U.S. history. The first installment, on how the storage industry has already improved its safety procedures, is available here . The grid battery fire in Arizona last year ended with an explosion, but disagreement has emerged on how exactly it began. Owner Arizona Public Service concluded that a defect in a single lithium-ion battery cell caused it to heat up, triggering a chain reaction that destroyed a whole rack and released gases that later exploded. But LG Chem, the manufacturer responsible for the battery cells and modules, published its own report with a different conclusion. According to LG Chem’s "progress report," compiled by scientific investigation firm Exponent, the physical evidence does not support the battery defect theory. The report , filed with Arizona's utility regulators last month, instead theorizes that external causes heated up the battery. At stake is the reputation of a long-time leader in the lithium-ion manufacturing space.