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Batteries are the Sound Choice for Better Hearing

People have been interested in better hearing for a very long time. As soon as there was aging, there was hearing loss. As soon as there were diseases to challenge the ears, and auditory function, there was hearing loss. The first power to help hearing was provided by an involuntary hand, cupped and raised to the side of the head. It was a simple attempt to capture more sound and bring it to the ear. We've come a long way since those humble beginnings!

We're in the age of silicon, and electrons, plastics, and precious metals. Now the power to hear is provided by an astonishing, sophisticated hearing instrument, and a carefully designed energy source, the zinc-air battery.

What makes all of this possible? A small, portable source of electricity, the hearing aid battery, often called a zinc air cell. Almost every hearing instrument uses a small zinc air button cell battery. It is the needs of the hearing impaired that guide the design and testing of zinc air cells. The zinc air cell is a tiny device that converts chemical energy into electrical energy. The voltage of the cell is characteristic of the anode material, zinc metal, and the cathode material, oxygen. The source of the oxygen is air. An electrolyte, which is conductive, and full of useful hydroxyl ions (-OH), permits the electrons to flow in an outside circuit as long as there is zinc metal left inside the cell. When all of the zinc has been discharged, zinc oxide is left, and the cell is done.

The zinc air battery is different from any other battery system because it contains only one of the electrode materials, the zinc. The other electrode carries only a small amount of oxygen, and when that is used, it looks for more from the outside air. That's why there are air holes on the bottom of the cell. They allow air to enter the cell as it is being used. The tab that is placed over the vent holes blocks air from entering and moisture from either entering or leaving, during the time that battery is in storage before the user needs it.

The zinc air battery could even be thought of as being half a battery and a half fuel cell. In a traditional battery all of the materials needed to make electricity are contained inside, including the source of the oxygen. In the case of a fuel cell, the reacting materials are brought together in the fuel cell only when electricity is needed. In the zinc air cell, the zinc and the electrolyte are added during manufacturing, but only the sophisticated air electrode is present. The air comes in later, entering the cell when it is needed. There's no air tank strapped on the side, it doesn't take up any extra room. That puts a lot of energy into a small, powerful package. You get electrons on demand and the power to hear.

Making a zinc air cell involves many different metals, plastics, and other materials. Each one must be carefully assembled because the materials in a battery always want to react with each other. They would, except that we keep them separated, so the only time they react is when an external circuit, such as a hearing aid, calls for the electrons to actually flow.

What materials find their way into a zinc air cell? Besides the zinc, there are parts made of nickel, iron, copper, chromium, manganese, carbon, nylon, PTFE, polypropylene, polyester, polyvinyl, potassium hydroxide, and high purity water. In order to put the most electrical energy into the small space available, parts are kept thin, and many parts perform several functions at once.

How has the demand on batteries changed?

The new technologies that drive the hearing industry are primarily the result of the digital revolution in electronics. Starting with computers, digital signal processing has now become a recognized means of analyzing an incoming sound, and almost instantly sending a customized signal to be amplified, to the output stage of the hearing instrument. This increases the power requirements of the whole instrument, and for the battery there is another demand. DSP circuitry will not function correctly if the voltage drops below a critical level, usually 1.05 to 1.1V.

The hearing aid wearer often wants a discrete, unobtrusive, and maybe even an invisible fitting. We all hear it, all the time.The smaller, the better, right?

The desire to make it smaller places an extra demand on the battery, because high performance instruments need to work very well, using the smallest battery possible. Adding features adds greater load on the battery and in so doing, the result could potentially be shorter battery life. Luckily, the quality and technology of batteries has been able to keep up with the smaller and more powerful demands of newer and better hearing instruments!

If you find that you are changing batteries more frequently, it may be due to a new activity, such as mall walking, where there is significantly more background sound being amplified. Remember, the battery is powering the hearing aid all the time, even when the wearer is ignoring the sound that is being amplified!

As younger people start to wear hearing aids, they will take them into more athletic and more environmentally challenging situations. Wearing hearing aids during a vigorous workout may be fine, but it exposes the hearing aids, and the battery, to that dangerous chemical, sweat! Once sweat gets inside the hearing aid, sweat can cause corrosion, damaging the contacts, and other tiny circuit components.

Users may want to try a drier (''dry aid kit'') for their hearing aid, although it really isn't necessary to put the battery in the drier. If the user feels the battery needs to be protected, the tab can be replaced. Under most conditions that extra effort isn't necessary. Re-tabbing is definitely advised if the battery is not going to be used for an extended period of time, such as a delay of a week or more.

Battery Clubs are available at many hearing healcthcare professional offices. Battery Clubs are a good way to buy hearing aid batteries because it helps you to make sure the batteries you purchase are fresh, and battery clubs usually help assure the best possible price!

The good news is that zinc air batteries give digital hearing aids the power to hear.

Visit www.rayovac.com to visit the Rayovac website.

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