A review of the benefits of using hearing aid drying devices to prolong battery life.

The Dry & Store hearing aid drying device was introduced in 1997.

Battery manufacturers are continually striving to meet the demands of today’s sophisticated hearing instruments. Power needs vary according to the instrument and also the listening environment. Batteries must be reliable, operating in a wide range of conditions. And of course everybody wants longer-lasting batteries. Zinc air is the most popular energy source across the board, but there is another factor in the competition for market share: how the end-user selects and uses the product.

Thumb through any professional journal or check out the battery carousel in your office or local drugstore, and it is clear that manufacturers are keenly aware that small batteries are difficult for the end-user to handle, and particularly so for those with reduced manual dexterity or impaired vision. In response to that challenge, we have seen a number of product design and packaging improvements in recent years, all intending to make these tiny powerhouses easier to handle.

Those improvements target battery replacement—the tasks of opening a package, activating the battery, and positioning it in the hearing aid. But what about the “in between” times, when the hearing aid is not in use? Specifically, what about hearing aid drying devices?

While more and more consumers use some sort of moisture removal pouch, kit, or appliance, they are hearing conflicting instructions about whether to leave zinc air batteries in during that drying period. With apology to the Great Muse, the question remains: “To dry or not to dry?”

Batteries generally dislike high humidity environments, but then again they do not like it too dry for long periods either. There is a compromise position that is good news for the consumer: it is OK to leave the batteries in for a cycle of Dry & Store conditioning or for a few hours in a passive nonelectrical drying kit. In fact, it may even help the batteries last longer. So now, there is no need to fumble with the battery until it is depleted and ready to be replaced.

 Storage of hearing aid batteries in certain hearing aid drying units can possibly prolong battery life.

Introducing the Product
When Dry & Store was first introduced in 1997, the operating instructions followed the prevailing protocol of the day: remove the batteries. However, we started to receive comments from the product’s users who admitted that they had not removed their batteries and seemed to be noticing longer battery life.

In a random survey of the product’s users, over half reported longer battery life. We believe there are likely several reasons for this:

• Zinc air battery performance can fall off dramatically in high-humidity environments. When moisture accumulates on and in a hearing instrument during the day, water can be absorbed into the zinc air cell. Our company’s hearing aid drying device removes that residual moisture, bringing the battery back into its nominal operating environment.

• Corrosion on batteries, battery contacts, and circuitry components can impede electrical current; a hearing aid drying device can prevent this type of corrosion.

• It takes less energy to drive the diaphragm of a microphone and/or receiver that is dry versus one that has taken on moisture.

• Regular use of Dry & Store hearing aid drying devices makes hearing instruments of all types (implant hardware included) work more efficiently. An efficient hearing aid needs less power, so the battery may last longer.

The phenomenon of longer battery life with Dry & Store use was confirmed by independent tests conducted by Eveready on its Energizer® zinc air batteries. The tests found that leaving the batteries in during Dry & Store conditioning caused no harm to the batteries; and in high humidity conditions, the process could potentially increase battery life by 10% to 20%.

Shortly thereafter, we changed our instructions and began recommending that users leave the batteries in during the product’s conditioning cycle.

Proponents of removing the battery during conditioning note that zinc air battery performance suffers when the operating environment is too dry. With an operating temperature of around 100 degrees (more or less, depending on the model) and relative humidity of 15% to 20%, Dry & Store is like a warm spring day in Phoenix. So, if people can use hearing aids and batteries in Phoenix, there is no reason why they cannot put them in a Dry & Store unit.

Rayovac shifted its position on the subject about 2 years ago, as noted in an article posted on Audiology Online, by Denis Carpenter, Zinc Air technical manager.1 In the article, he states that low humidity does cause the cell to lose water, so if you dry out an already-dry battery, it would shorten battery life “most noticeable if your typical service life is more than 10 days.” He adds, “A dry aid kit may be beneficial for your battery, however, if you normally use your aid in a high humidity environment. The drying that occurs in the dry kit can counteract any excess water intake due to the humid environment that can shorten battery life.”

A Humid Environment
Considering that the relative humidity of the ear canal has a tendency to be moderately high, add a hearing aid to block the escape of any moisture, then throw in a “sweat factor” associated with an active lifestyle, and it is not hard to imagine that hearing aids and batteries often operate in a humid environment. In any case, it would appear that individuals who have the most issues with hearing aid moisture will likely gain the most benefit from leaving their batteries in during the drying process.

Norm Ryan, while manager of technology and business development for Energizer Batteries, notes that Eveready had “researched this a couple times. We have tried to determine whether dry-aid kits do take the moisture out of the hearing aids if stored in them overnight, but more importantly, to see how batteries are affected by the dry-aid kits. Our results show the hearing aids do dry out a bit in the dry-aid kit and, interestingly, the battery life is usually improved if left in the aid or placed in the kit with the aid. So yes, the dry-aid kits work, and they are worth using on a regular basis.”2

We should note that these points relate to zinc air batteries as opposed to those with a closed system. Sealed and/or rechargeable batteries would not be impacted by moisture and thus would not benefit from the drying process.

Also, there are a number of heated boxes that recommend battery removal. In the case of Dry & Store, the heat is just a few degrees warmer than body temperature, so there is no detrimental effect. But since other devices operate differently, it is best to follow the instructions that accompany each appliance.

Given that moisture is one of the biggest causes of hearing aid repairs, it is good to know that daily, preventive maintenance of hearing aids does not have to require fumbling around with those tiny batteries. No more hiding loose batteries from Fido or Fluffy, and no more crawling around on hands and knees searching for the “battery that got away.”

Katy Pindzola is manager of marketing and project development for Ear Technology Corporation, Johnson City, Tenn.

References
1. Carpenter D. Audiology Online; July 2003.
2. Beck D. Battery operated dry aid kits? An interview with Norm Ryan. Healthy Hearing. August 11, 2003. Available at: www.healthyhearing.com/library/ate_content.asp?question_id=157.) Accessed September 20, 2005.