Differences in rust in hearing aid batteries across four manufacturers, four battery sizes, and five durations of exposure.

Three hundred twenty zinc-air batteries representing four manufacturers (Energizer, Power One, Duracell, and Ray-O-Vac) and four cell sizes (10, 312, 13, and 675) were exposed in a salt spray fog apparatus for 2.5, 5.5, 24, 48, and 72 hours.