Tech Topic | October 2015 Hearing Review

A futuristic look at power sources and what it may eventually mean for hearing care.

The range of rechargeable options in electronic products has been amazing…except in hearing aids, says the author. He predicts that we are approaching a technological tipping point where this will change, bringing an array of rechargeable hearing devices to our market.

It’s probably a safe bet that somewhere in your home or office you have samples of a remarkable energy conversion system. Just add a little water and sunlight and­—“Ta-Dah!”—those green plants turn photons into chemical energy for growing leaves, fruit, and food for the animal kingdom. And, after a few million geological years or so of depositing organic material onto the earth’s crust, they have also created the carbon fuels that run our techno-frenzied society.

Roughly 2 billion years ago, plants, following the lead of bacteria, acquired the alchemical wizardry to build a nifty protein catalytic converter system to use sunbeams, stripping hydrogen and oxygen atoms out of water, and spooning in dabs of carbon dioxide from the air to make sugars—while releasing batches of 02 to the considerable advantage of air-breathing and sugar-consuming animals like ourselves.

In sunny Colorado, where I live, an array of photo-voltaic (PV) panels can robustly supply most of a small household’s power needs. However, those technologies are far less impressive in design than the potted plants in your living room. For hearing aid users, such as myself, it’s a bit perplexing that tiny green chloroplasts can work as energy capturing cells to support the entire planet, yet millions of consumers in need of a boost in audibility still struggle and juggle with little metal discs in their hearing aids to power the amplification they need for everyday conversations.

With support from the US Department of Energy, there are numerous exciting developments in the field of Biomimicry, suggesting some forms of artificial photosynthesis are moving towards feasible realization.1 Likewise, rechargeable electronics dominate our world.

A typical hearing aid consumer has plenty of experience with mobile phones, digital cameras, laptop and tablet computers, wireless headphones, etc, none of which require regular opening of small battery drawers and persistent removal, disposal, and replacement of tiny button cells. The rechargeable power supplies of most consumer devices are sealed and easily coupled to charging sources throughout the home by universal serial buses (USB) of various sizes.

Unfortunately, the requirement for replaceable hearing aid batteries seems to have lingered well past the engineering advances common to other small electronics that similarly require low-voltage electrical power. For a generation of Baby Boomers who have experienced massive techno-change, this just seems “so 20th Century!” But even the oldest hearing aid consumers have relatively strong opinions on the matter; a recent survey of 100 hearing aid users in Colorado showed that over 86% of respondents would prefer not to have to change or throw away batteries, including respondents aged 80+.2

There have been numerous introductions of rechargeable batteries over the past several decades. Some seemed to operate reasonably well…for the first few months. But the Nickel Cadmium cells (NiCd) of the 1970s and 1980s tended to behave unfavorably after some ill-defined discharge and recharge cycles. Use-time declined to progressively shorter operational hours, largely attributed to “memory effects.” Nickel metal was also later compounded with hydride in the generally superior NiMH cells, but consumers and dispensers were still largely unenthused, perhaps due to the requirement of the charging units and/or the perceived cost per cell.

New Approaches

Chemistry and technology have advanced, and there have been numerous attempts to relieve the burden of battery manipulation, as well as solve supply constraints in developing parts of the world that lack easy replacement sources. On the creative edges, one approach sought to capture energy from the dynamic motion of the mandibular joint.3 Engineering modeling estimates that the chewing of one medium-sized hamburger could generate enough charge to power a hearing aid for roughly 2 hours!

Also on the edgy periphery are efforts to generate safe wireless recharging of implanted devices, such as cochlear implants, by such through-the-body approaches as ultrasonic piezoelectric techniques.4 Meanwhile more mundane, but probably more pragmatic, work has produced advances in materials and chemical science towards rechargeable batteries with new formulations of metals including, sodium, grapheme oxides, aluminum compounds, and a nano-sandwich of molybdenum atoms.5,6

For hearing aids specifically, silver zinc compounds and one of several lithium-ion polymers have been introduced.7 The reader is referred to Peanteado and Bento8 who published in 2013 a comprehensive, but now slightly dated, comparative study of currently available hearing aid batteries.

Technological Acceleration

Given the relatively slow pace of rechargeables into the hearing aid market, it is understandable if the reader is skeptical that any change in power sources is imminent. But it may also be wise to look around at how many other unexpected changes have entered the mainstream in recent years. For example, who would have predicted that mobile phones would be on sale in grocery stores or the 7-Eleven?

So-called “futurists” know quite well that the very pace of change itself is in a continuous state of acceleration. Generally, changes occur as either a percentage, like the growth of GDP of around 3% in a healthy economy, or by some exponent like X2. Exponential growth is often remarkably deceptive and sometimes bewildering.

Figure 1

Figure 1. Classic case of exponential growth. The number of days for one lilypad to propogate to a point where the entire area of a pond is covered by lilypads.

One classic illustration that may apply to steadfast developments in materials sciences and changes in power sources is the “Lily Pad story” (Figure 1). A pond is becoming populated with fast-growing lily pads. The surface coverage of the plant doubles every day (ie, growth of X2). If the entire pond is covered with pads on Day 30, goes the lesson, on what day is just one half of the pond covered? The answer, to the surprise of some, is Day 29.

This tale, often put forth as an ecological wake-up call, is perplexing to many because of what’s occurring in the first 25 days or so. Alarms are not sounded because the early portion of Figure 1 does not attract attention. At Day 26, still well less than 10% of the pond has lily pad coverage.

The Long Pursuit of Power Storage

Since Count Alessandro Volta’s seminal work in 1800 to develop a battery and the first practical use of electricity, there has been a passionate and long pursuit to advance storage technology.9 The quest has basically been to determine how the energy of flowing electrons could be held in readiness for release on demand. Solid-state batteries, such as those used in hearing aids, are essentially variations of the fast iterations of power capture methods, including hydro power, wind power, fly wheels, and thermal variations right down to a coffee thermos that stores heat energy by design. Battery technology is a classic example of the productive output and commercialization of continuous pure research in chemical and materials sciences. It is not at all unreasonable to assume that Days 1 through 25 have passed in this transformative quest. The next iterative advances may well push the curve of change upwards much more rapidly towards what consumers of the 21st century hearing aids will expect—devices without the need to remove and dispose of batteries.

A New Leaf of Change?

A version of a lithium ion sealed power supply hearing aid was recently introduced (Figure 2). A micro-USB connector fully charges the IMH Corporation’s 8-channel, 4-Memory, programmable small BTE (with noise reduction) in approximately 90 minutes for operation between 16 to 20 hours (

Figure 2

Figure 2. A BTE hearing aid from IMHear that uses a USB port for recharging its battery.

Since Li-ion batteries have higher voltage than the typical 1.2V requirement of hearing aids, a proprietary conditioning circuit is implemented in an efficient control design. It’s possible this product is representative of day 25 or 26 on the curve of inevitable change in product exchanges between professionals and hearing aid impaired consumers. Time, of course, will weigh in on that speculation.

It’s been a long and winding path from Volta, James Watt, Georg Ohm, James Joule, and others to pushing millions of electrons per second into controlled amplification for hearing deficient consumers’ benefit. To many tech-savvy age 60+ consumers, it also seems improbably overdue to design hearing aid power supply sources in line with their numerous other devices that are conveniently free of battery changes and the eco-ethical distress of disposal.

Some are willing to bet that these behaviors will be rendered historic in the near future. The introduction of the Apple Watch has created a vigorous rush towards wireless rechargeable developments which are expected to grow by 4,000% in the next 9 years.10 Tellingly, the retailer Ikea is now selling desks and tables with built-in inductive charging surfaces.

The rapid pace of change in parallel industries in support of hearing aid manufacturers’ supply chains almost certainly shortened the timeline to the introduction of digital devices.11 Hence, the goal of placing increasingly tiny chip sets with sensors for wireless computations in ever-smaller wearable devices is likely to impact the trajectory of change in the relatively small hearing aid industry. That’s why some are convinced that a kind of “battery free” experience for users of ear-level amplifying devices is not that far in the future.

Of course, there will still be batteries, but they will be—as they should be—untouchable. Perhaps consumers will simply lay their hearing aids on their wireless charging nightstand next to the smart phone, and on sunny days let the array of houseplants go to work.


  1. Yarris L. Major advance in artificial photosynthesis poses win/win for the environment. April 16, 2015. Available at:
  2. Schweitzer HC. Eco-Friendly innovations in power supply for hearing aid users. Paper presented at: American Academy of Audiology’s annual AudiologyNow!2015, San Antonio; March 2015.
  3. Energy harvesting from jaw movement to power hearing aids. July 8, 2014. Available at:
  4. Acoustical Society of America (ASA). Medical implants: Tune in, turn on, power up. Dec 4, 2014. Available at:
  5. Lin MC, Gong M, Lu B, et al. An ultrafast rechargeable aluminium-ion battery. Nature. 2015;520:324–328 doi:10.1038/nature14340
  6. Van Noorden R. The rechargeable revolution: A better battery. Nature. 2014;507:26-28. doi:10.1038/507026a
  7. Schweitzer HC. Good for the planet, but hearing aid professionals will have to reboot (again). Feb 17, 2015. Available at:
  8. Pentaeado SP, Bento RF. Performance analysis of ten brands of batteries for hearing aids. Intl Arch Otolaryngol. 2013;17(3):291-304.
  9. 9 Schweitzer HC, Smith DA. From horsepower to hearpower. Hearing Review. 2009;16(7):10-15. Available at:
  10. Green D. 2015 set to be a breakthrough year for $1.7 billion wireless power industry. March 31, 2015. Available at:
  11. Schweitzer HC. Future trends in amplification. In: Valente M, Hosford-Dunn H, Roeser R, eds. Audiologic Treatment. New York:Thieme;2000:715-728.


Christopher Schweitzer, PhD

H. Christopher Schweitzer, PhD

Christopher Schweitzer, PhD, is chief of technical audiology for IMHear Corp, Downers Grove, Ill, and owner of Family Hearing Centers of Colorado.

Correspondence can be addressed to HR or Dr Schweitzer at: [email protected]

Original citation for this article: Schweitzer HC. Batteries in Your House Plant? Hearing Review. 2015;22(10):32.