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. At the conclusion of each exposure, the batteries were rated blindly for the presence of rust by four experienced audiologists using a four point rating scale. Results revealed significant differences in the rating of rust across the four manufacturers and duration of exposure. No statistically significant difference was found across cell size. Also, the correlation between raters was exceptionally high indicating that each audiologist rated the presence of rust for each battery in a very similar manner. Scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDS), and Auger electron spectroscopy (AES) techniques were applied and provided answers for the observed differences in rust between the four manufacturers.