Lithium-Ion Rechargeable Battery Limitations Emerge
What happens when your rechargeable hearing aids hit the wall?
Presented by ZPower
16 July 2019
Lithium-ion batteries are classified as "dangerous goods" by the International Air Transport Association (IATA).
Rechargeable hearing aids are here
When rechargeable hearing aids and consumer earbuds with lithium-ion battery technology first hit the market in 2016, they achieved rapid consumer acceptance.
The new hearing aids finally offered what many users had long been waiting for. There was no more fumbling to replace tiny disposable batteries every few days. And there was no need to carry extra batteries around. Best of all, you could simply charge your hearing aids while you slept, and they’d be ready to wear by morning.
And beyond those practical benefits, lithium-ion rechargeable technology had become fashionable. In 2016 Apple introduced its AirPod earbuds, powered by lithium-ion rechargeable batteries, and in no time they were everywhere.
Holding a charge in the rechargeable-earbuds era
But now, three years into the rechargeable earbud era, some limitations of lithium-ion technology are starting to emerge. For instance, buyers of the original Apple AirPods have started to complain that the rechargeable batteries in their earbuds won’t hold a charge as long they used to. And they're finding that it's not easy to replace those batteries.
This isn’t a problem with the Apple AirPods technology, but a problem that occurs with all lithium-ion batteries. The fact is, lithium-ion batteries start losing capacity the first time they are recharged, and this capacity loss continues with every charge cycle.
There are also safety concerns. Lithium-ion batteries contain toxic substances, and they can spontaneously combust when damaged. So, device manufacturers make them inaccessible by sealing them into the devices. Customers with less than two- or three-year-old batteries that have worn out and no longer hold a charge must send their devices back and pay for battery replacements or purchase a new device.
The same issues are coming into play with lithium-ion-based hearing-aid batteries. Especially since it has been about three years since the launch of the first lithium-ion rechargeable hearing aids, and users are draining battery power at ever-increasing rates with endless hours of streaming wireless smartphone audio into their hearing aids.
ZPower's silver-zinc rechargeable hearing aid batteries work with hearing aids that also accommodate standard disposable batteries.
Rechargeable hearing-aid technology options
Hearing aid manufacturers are working hard to develop new and improved rechargeable hearing aid options. In many instances they are finding that an alternative—silver-zinc rechargeable battery technology—overcomes some of the current limitations of lithium-ion batteries.
There are three technology options for rechargeable hearing aids, but only two of them meet the current size and power management requirements of hearing aids.
- Nickel metal hydride (NiMH) hearing aid batteries have been around for more than a decade. However, due to their limited capacity and the ever-increasing energy demands of advanced hearing aids, these batteries do not have enough energy to last a full day.
- Silver-zinc and lithium-ion hearing aid batteries have ushered in the new era of rechargeability for hearing aid users. Both technologies offer greater daily and overall battery life than NiMH batteries. And both offer higher energy density than NiMH batteries. However, silver-zinc chemistry offers higher energy density than lithium-ion micro-batteries. This leads to a size advantage: silver-zinc rechargeable batteries can be made small enough to be used with hearing aids that use size 312 batteries, whereas lithium-ion batteries cannot. And silver-zinc offers longer run time in similarly sized batteries.
Advanced hearing aid features drain power
Digital hearing aids are getting better all the time, but nearly every new feature providing clearer custom sound also drains more power. For instance, technologies such as noise suppression and feedback cancellation continuously monitor and process sound on the hearing aid's built-in chipset. Active, ongoing processes like these increase power consumption and lead to higher battery drain.
Wireless streaming is another technology that consumes a lot of power. Made-for-iPhone and Android hearing aids have been a huge hit. They have made wireless streaming of smartphone audio a "must-have" feature for many hearing aid wearers. But a significant amount of energy is used every time you stream audio from your smartphone, TV, iPad, or other wireless accessories.
Wireless streaming is also required for your left and right hearing aids to "talk" to each other. Many hearing aid pairs maintain a constant wireless connection to provide adjustments delivering more comfort and benefit in noisy environments. But the more they stream, the more they drain the battery.
Rechargeable hearing aids tailored for different user needs
With such a broad potential mix of advanced features, there are different hearing aids with features optimized for different user needs. For example, a person with a more pronounced hearing loss may require more feedback cancellation than someone with less hearing loss and may use additional power-draining features that shorten battery life. Or someone with mild hearing loss, but who wants to use hearing-aids as earbuds for listening to music, will use a lot of battery power streaming audio.
Manufacturers meet these various needs by offering rechargeable hearing aids optimized for different user requirements. NiMH rechargeable technology falls short of meeting most power requirements of advanced hearing aid features. But lithium-ion and silver-zinc technologies deliver the power that hearing aid users need.
In fact, several manufacturers offer both lithium-ion and silver-zinc rechargeable technologies in their hearing aids, depending on what features users need most.
And makers of specialty hearing products are finding that silver-zinc rechargeable batteries help them achieve smaller form factors. Bose Corporation’s noise-masking sleepbuds provide soothing continuous sounds that block exterior sounds in addition to masking interior ringing and hissing from tinnitus. They fit within the ear comfortably, in part because they utilize very small silver-zinc rechargeable batteries from ZPower.
Bose SleepBuds use very small silver-zinc rechargeable batteries from ZPower.
Silver-zinc rechargeable hearing-aid solutions
Silver-zinc batteries in hearing aids operate on a lower voltage than lithium-ion batteries and are non-flammable. Therefore, they are safe to handle, and there are fewer risks if swallowed or ingested by children or pets.
Since they are so safe, silver-zinc hearing aid batteries are often designed to be removable from the hearing aid case and are interchangeable with disposable zinc-air batteries. That means hearing aid users who sometimes don't have access to an electrical outlet can use disposable batteries as a backup to their silver-zinc rechargeable batteries. And because of silver-zinc’s high energy density, it is possible to design the smaller, more discreet rechargeable hearing aids.
Since all rechargeable batteries lose capacity as they are recharged, all rechargeable batteries must be replaced at the end of their life. Thankfully, hearing aids that use silver-zinc rechargeable batteries do not need to be sent back for service when the battery can no longer be recharged. The battery can simply be replaced by the hearing aid wearer. This extends the useful life of the hearing aids and allows the owner to maintain a consistent battery capacity for the life of their hearing aids by replacing the battery when needed.
Lithium-ion rechargeable hearing-aid solutions
Rechargeable hearing aids with lithium-ion batteries are popular with consumers who no longer want to insert and remove their hearing-aid batteries. They are designed to supply all-day power, and they can be easily recharged overnight.
But because lithium-ion batteries contain toxic materials and run the risk of combustion if handled improperly, they are not consumer replaceable. So, it's impossible to use traditional disposable hearing aid batteries as backups when the rechargeable batteries run out of power.
Also, due to a lower energy density, lithium-ion rechargeable batteries are larger than silver-zinc batteries. Rechargeable hearing aids that rely on lithium-ion batteries also require safety circuitry, which increases overall size and bulk of the hearing aids. As such, it is difficult to deliver the kinds of small, near-invisible hearing aids that many users desire.
And as with the Apple AirPods, when lithium-ion rechargeable hearing-aid batteries inevitably wear out, the consumer must return them to the manufacturer to have the batteries replaced. This is a big concern for hearing aid wearers, as being without ones hearing aids can mean a temporary interruption of normal communication with loved ones and colleagues.
Shipping products with lithium-ion batteries is not simple either. Lithium-ion batteries are categorized as dangerous goods and are subject to special packaging, labeling, and shipping restrictions.
The rechargeable hearing aid future
Starting in 2016, rechargeable hearing aid battery technology finally started delivering a combination of features that met the power and functionality requirements of consumers who no longer wanted the hassle and complexity of disposable batteries. Lithium-ion rechargeable technology, already found in many other consumer products, was a natural first choice for many of the first rechargeable hearing aids. Lithium-ion powered hearing aids can be expected to continue improving by delivering longer product life, more hours of power from an overnight charge, and smaller form factors.
But as consumers have seen with their AirPods, hearing-aid owners will start to confront limitations of lithium-ion rechargeable technology. The alternative delivered by silver-zinc rechargeable technology is increasingly attractive to consumers who seek smaller product sizes, the ability to swap out their rechargeable batteries with disposable batteries, and/or easy battery replacement when the battery wears out.