PERFECT SIZE: These size 312 brown hearing aid is most commonly used in the smaller BTE devices and very popular for in-the-ear hearing aids. LONG LIFE: These hearing aid batteries offer reliable performance and long durability with very good price-performance ratio. The shelf life of these batteries is up to 4 years. PACK OF 20: This pack of size 312 brown 1.45V hearing aids includes 120 hearing aid batteries. Each button batteries measures 7.8 x 7.8 x 3.6mm and weighs 3g. ZINC AIR: These batteries with modern zinc-air-technology (1.45V) are air-activated, the sealed sticker allows them to remain inactive until removed. Once peeled off the battery, oxygen will interact with zinc in battery and activate. Wait at least 1 minute after removing the sticker to fully activate before placing it in the hearing device. RELIABLE REPLACEMENT: This pack of reliable high-quality size 312 brown hearing aid button batteries is the ideal replacement energy source for hearing aids and hearing aid sound amplifiers. These batteries are also mercury-free making them great for the environment!.