by Barry A. Freeman, Ph.D.
Battery Life Counseling – With Consideration of Rechargeable Batteries
Barry A. Freeman, Ph.D.
The recent series of articles on batteries and battery life in Wayne’s World brings to light one of the least understood and, perhaps, most important patient counseling and management issues faced today by those dispensing and wearers of hearing aids—battery life counseling. The technology advancements of contemporary hearing aids have led to greater satisfaction and adoption by patients but have increased the burden on those who fit hearing aids to properly counsel patients on performance such as battery life. New hearing aids have wireless streaming capabilities with features to manage feedback, provide ear-to-ear communication, and improve performance in challenging listening environments. In addition, they offer the convenience of wirelessly streaming Apps for phone conversations, music, and games. While advantageous to the patient, these advancements increase the power requirements necessary to operate the hearing instruments.
In EuroTrak (2009-2015) surveys of patients in Europe, it is reported that patients typically wear their hearing aids an estimated 8 hours per day. In the U.S., MarkeTrak IX (2015) reports average wear times closer to 12 hours per day. So, then, how should patients be counseled relative to expected battery life?
Manufacturer specification sheets report the average drain on batteries from hearing aid usage is ~1.2 mA. Based on formulas provided in a recent Hearing Health and Technology Matters article, using 1.2 mA as the average current drain for a size 312 disposable zinc-air hearing aid battery with a capacity of 180 mAh, should last 105 hours*. In Europe, where EuroTrak estimates that patients wear their hearing aids 8 hours per day, the calculated battery life should last 13.35 days. In the U.S., with 12 hour daily wear-times, a battery should last 8.75 days.
Wait, you say, my patients seem to be using way more batteries! Suppose, for example, you agreed to give your patients a one year supply of batteries with the purchase of their new 2.4GHz wireless streaming hearing aid using 312 batteries? According to the manufacturer’s specifications, average U.S. wear time, current drain of 1.2 mA, and battery capacity (180 mAh), you would estimate that your patient would need about 42 batteries per year (a new battery every 8.75 days for one year). Yet, we know that many patients are using 2-3 times that number of batteries. What is going on?
For the past year, I’ve been working with the engineers and chemists at ZPower, the world’s leading manufacturer of rechargeable high capacity hearing aid batteries, to understand the average wear time and capacity needs of patients wearing wireless hearing aids. We, also, wanted to know what was going on so that we could design and manufacture a rechargeable battery that would last a full day in wireless streaming hearing aids.
Wear Time Examples
A first need was to understand the wear times of patients, and then to understand the actual battery current drain of hearing aids. For most of the past year, ZPower has been running clinical field trials at major medical centers and independent practices with their rechargeable battery system. This system is designed to permit hearing aid dispenses to retrofit new and existing hearing aids and make them rechargeable in the office simply by replacing the battery door and inserting a ZPower silver-zinc rechargeable battery. Field trial patients are provided with a Data Collection Module (DCM) that tracks and monitors the average wear time of the hearing aid and battery use. It is ZPower’s version of data-logging, but specific to hearing aid and battery utilization. Figures 1-3 are examples of typical hearing aid wear times of patients fit with different wireless streaming hearing aids that are using the ZPower Rechargeable 312 battery. In Figure 1, the patient wore the hearing aid for 15-18 hours per day on a single charge. The average charge time was 3-4 hours. Figure 2 is a patient that wore a 2.4 gHz wireless streaming aid 15-20 hours per day with minimal streaming on a single ZPower rechargeable silver-zinc 312 battery. Figure 3 is a patient who consistently streamed from his iPhone™ 3-4 hours per day and wore the hearing aid 15-16 hours per day with the ZPower 312 silver-zinc rechargeable battery.
Figure 1. Average wear and charge times for a patient wearing a wireless streaming BTE hearing aid fit with the ZPower Rechargeable System. The Y-axis is presented as a daily clock with 0:00 representing midnight. The green bars are the time the hearing aid was in a charger being charged; the yellow bars are the time the hearing aid remains in the charger, not charging, but waiting to be turned on; and the blue bars are actual wear times, with the numbers representing the hours used.
Figure 2. Estimated wear time of patient fit with 2.4GHz wireless streaming hearing aid with the ZPower Rechargeable System with 312 ZPower battery. Patient was a self-defined ‘light streamer.’ The patient wore the hearing aid 8-10 hours per day on a single charge (black bars). The remaining capacity (in mAh) in the battery after an average day is shown with the green bars.
Figure 3. Patient who streamed an average of 3-4 hours per day from his iPhone or other products. Wore hearing aid with 2.4GHz wireless streaming and Rechargeable System for an average of 14-16 hours per day (black bars). The remaining capacity in the battery at the end of each day is represented by the green bars (in mAh). The data collection module includes an algorithm that calculates remaining voltage and converts it to remaining capacity.
The patients in these field trials were not atypical and wore their hearing aids more than 12 hours per day. In some cases, when asked, they explained that they no longer had to worry that their hearing aids would go dead in the middle of the day or when at a meeting or a movie. They had the confidence that with the rechargeable battery, the hearing aid would be powered for a full day without hearing a low battery warning signal. Recall, in MarkeTrak IX, when non-owners of hearing aids were asked what features they wanted, rechargeability was on the top of their list. Patients want to wear rechargeable hearing aids.
From field trials, ZPower discovered that a battery with more capacity had to be manufactured. Initially, the rechargeable battery was designed to meet the capacity needs reported by the hearing aid manufacturers. However, it soon became clear that hearing aids were consuming much more capacity than reported on their datasheets. As Jorgensen et. al. (2013) reported, “there is little correlation between datasheets…and measured real-life current consumption.” The information on manufacturer datasheets is run in accordance with ANSI standards which require hearing aid features to be turned off. Basically, the hearing aids are running in operating life mode.
Hearing Aid Current Drain Differences Among Hearing Aids Using Streaming
In order to gain a better understanding of the actual current drain of hearing aids, a series of wireless products were evaluated in engineering labs at ZPower. Figure 4 presents the current drain of hearing aids as reported on the datasheets, with manufacturer first-fit features like noise and feedback management activated, and with streaming. Note with hearing aids using far-field 2.4GHz streaming, the current drain can average 4.5 mA and exceed 5.0 mA. With near field magnetic induction (NFMI) streaming that uses an intermediate relay with its own power source for streaming, the consumption is less but still can exceed 2.0 mA.
Figure 4. Power consumption of hearing aids in mA representing different companies (A, B, C. D). Comparison of manufacturer datasheet (blue bars); first-fit wireless features activated (red bars); streaming (green bars).
The clinical implications of this information are broad and important to audiologists, dispensers, and their patients. For example, if one of the hearing aids of a patient who is wearing binaural wireless streaming hearing aids with ear-to-ear communication goes in for repair, the other hearing aid will spend the day searching for its pair, and battery life will plummet. In the case of wireless CROS and BiCROS hearing aids, the battery on the transmitter-side hearing aid (dead ear) will drain much more rapidly because it takes a lot more current to transmit than to receive.
The key is to understand the hearing aids that are being fit. Understanding this will enhance your counseling and will build a relationship of trust with your patients.
*HHTM has chosen to use the battery life formula (A), rather than the simplistic formula (B) that is often used. A full explanation for this will be made in a following post on this site under Wayne’s World.
Barry A. Freeman, Ph.D. is Vice President of ZPower Battery, LLC. He was founding Chair of the Audiology Department and a Professor of Audiology at Nova Southeastern University. Before that, Dr. Freeman owned and practiced for twenty years at the Center for Audiology in Clarksville, TN and Hearing Services of Kentucky in Hopkinsville, KY. Dr. Freeman earned his Bachelor’s degree in business and economics from Boston University and completed his doctorate in Hearing and Speech Science from Michigan State University.
He is a past-president of the American Academy of Audiology and served on the Academy’s Board of Directors for six years. He currently serves as VP for Professional Activities for the Florida Academy of Audiology and as a member of the Advisory Board of the Accreditation Commission for Audiology Education (ACAE). He received the Distinguished Achievement Award from the American Academy in 2006.
References
Abrams HB, Kihm J. An Introduction to MarkeTrak IX: A New Baseline for the Hearing Aid Market. Hearing Review. 2015;22(6):16.
EuroTrak 2009-2015. Available at: EHIMA Documents
Joergensen, H.S., Baekgaard, L, and Bendtsen, B., Battery consumption in wireless hearing aid products. AudiologyOnline, February, 2013.
