Hearing aid batteries are more complicated than you might suspect. Even a long-time hearing aid user may learn a few new things from this article.
Batteries for hearing aids are typically zinc air cells. They are small, one-time-use, disposable cells that require oxygen to work. The only exception to this is the rechargeable batteries.
Hearing aid batteries come in many sizes and can be distinguished by the standardized color coding system and the numbers. In order of size from largest to smallest the following are the common batteries seen in hearing aids today; size 675 is blue, size 13 is orange, size 312 is brown and size 10 is yellow. The color system is seen in the color of the packaging as well as the color of the stick tab on each cell.
As stated the batteries are zinc air and this distinguishes them from any other battery commonly used in our households. Zinc air batteries are activated by the oxygen in the air. Without oxygen the batteries cannot function.
When the sticker (or tab) is removed from the back of a cell the battery is slowly powered up as oxygen is gathered around and absorbed into the small holes on the battery. If you look closely you can see these holes. The holes are small to prevent the battery from leaking "battery juices" but large enough to allow a molecule of oxygen to permeate. There is also a filter behind that hole to prevent leakage and that filter will allow oxygen to permeate, although it does slow the absorption.
Because the process of oxygen absorption is not immediate, battery companies recommend that you wait one full minute before inserting the battery into the hearing aid and closing the battery door. If you do not wait that full minute, the battery may not have sufficient oxygen to power up and it can be starved for oxygen inside the hearing aid's casing. This instruction can sometimes be seen on the battery packaging.
This tip is little known or understood among hearing aid users and healthcare professionals. The fact that battery cells can starve for oxygen was not as likely in older model hearing aids so the issue was not often brought up. But newer hearing aids on the market are more air tight in an attempt to help reduce moisture related problems (sweat, humidity, water, rain, etc) and to make the hearing aids more water resistant.
I gathered much of this information from a discussion with my battery supplier. Being an audiologist I have the fortunate opportunity to learn from all the industries that deal with hearing aids and hearing aid related products. I am happy to pass this information along to the general public and my patients.
This blog posted by Suzanne Yoder, Au.D. Doctor of Audiology and owner of HearWell Center. Please visit our website for more information http://www.hearwellcenter.com/ 
