How long will the battery last? This is one of the most frequently asked questions from hearing aid wearers, most likely because battery life plays a significant role in the everyday handling of hearing instruments. To many hearing aid users, having to replace the battery once or twice a week can be a perceived hassle and/or unwelcome expense. In fact, a recent MarkeTrak survey (Kochkin, 2010) revealed battery lifetime to be the physical hearing aid feature to receive the highest percentage of negative ratings.
So, what do you tell your patients when they ask? Do you look at the manufacturers’ datasheets or make an educated guess? Unfortunately, there is no easy way to tell how long hearing aid batteries will last in a given instrument, so providing your patients with a precise answer is not always possible.
This article reports a series of measurements which show that the real-life battery consumption of state-of-the art commercially available wireless hearing aids is not accurately reflected in the standardized measurements reported on the manufacturers’ datasheets. More often than not, real-life performance deviates notably from the standardized datasheet figures when adaptive features, such as feedback canceling, noise reduction, and other features are activated. Moreover, it is evident that the wireless streaming options available in modern digital hearing aids may increase the battery consumption quite dramatically. For some hearing aids, the difference between the current consumption measured during normal use and in streaming mode more than doubled.
The data reported in this article result from a test of six of the most recent commercially available high-end wireless hearing aid products (Figure 1). With one exception, all are receiver-in-the-canal or receiver-in-the-ear (RIC/RITE) style aids targeting mild to moderate hearing loss, and all use a 312 battery. Some manufacturers offer their wireless solutions in behind-the-ear (BTE), RIC/RITE- as well as in-the-ear or completely-in-the canal (ITE/CIC) solutions, while others offer only wireless solutions for some of these models. To allow for a straightforward comparison, wireless instruments included in the test had to be comparable both in terms of performance point (high end), model, battery size, and target hearing loss.
Figure 1. Wireless hearing aids and accessories included in field test, in alphabetical order.
Why you Cannot Rely on Datasheet Figures
In theory, calculating the expected battery life in hearing aids should be simple. Two basic figures are needed, both of which should be available on the datasheet of a given hearing aid: the battery capacity in milli-Ampere-hours (mAh), and the current drain of the hearing aid in milli-Ampere (mA).
To give an example, a wireless hearing aid that runs on a 312 battery might have a current drain of 1.1 mA. The 312 battery in question has a capacity of 145 mAh. The battery life is then calculated as:
Capacity /Drain = Battery life
145 [mAh] /1.1 [mA] = 132 [hours]
However, real life battery life is not so straightforward to calculate. Datasheet information on current consumption is defined according to the International Electrotechnical Commission (IEC) standard (60118-0 or 60188-7) or the ANSI S3.22. This standard procedure, which is followed by the hearing aid industry in general, involves measurements made in a special test mode which usually involves the turning off of important features like feedback canceling, directional microphone systems, and wireless functionality. Some manufacturers, therefore, offer an indication of expected hours of use in addition to the standardized measure. This figure should ideally offer a more precise indication of what the wearer can expect in terms of battery life when these processing functions are active. The indicated current consumption (IEC 60118-0 standard) and the expected hours of use for the most recent wireless hearing aids from the six largest manufacturers in the industry are shown in Figures 2 and 3 below.
Figure 2. Current consumption as stated on datasheets for 6 comparable wireless hearing aid products (from best to worst).
Figure 3. Estimated real-life battery lifetime/hours-of-use as stated on the datasheets. One manufacturer does not provide this information. If the manufacturers’ datasheets indicate a range, the smallest value is included in the figure.
A third complication is that the expected hours of use are not based on the same battery capacity across manufacturers. A comparison of Figures 2 and 3 above quickly reveals a considerable variation in the presupposed battery capacity; ranging from approx. 120 mAh to as much as 160 mAh in order for the current drain and the expected hours of use to correspond.
For example, hearing aid manufacturer C’s indicated current drain is 1.2 mA, and the expected hours of use 133. This requires a battery with a capacity of 160 mAh.
Capacity/ Drain = Battery life
160 [mAh]/1.2 [mA] = 133 [hours]
On the other hand, hearing aid manufacturer A’s indicated current drain is 1.0 mA, and the expected hours of use 120. This requires a battery with a capacity of 120 mAh.
Capacity/ Drain = Battery life
120 [mAh]/1. [mA] = 120 [hours]
The variation in presupposed battery capacity is illustrated in Figure 4 below. Note that the calculation cannot be done for manufacturer B, because expected hours of use are not stated on their datasheet.
Figure 4. The variation in presupposed battery capacity among five hearing aid manufacturers. The calculation cannot be done for manufacturer B, since their datasheet does not state expected hours of use.
How to Obtain a Uniform Measure of Battery Consumption across Products using Datasheet Information
In order to make a comparison across products using the manufacturers’ datasheet information the battery capacity must be held constant. For example, by assuming that a battery with the same capacity of130 mAh is used in all the products, the calculated hours of use based on the manufacturers’ reported current drain would be as shown in Figure 5.
Figure 5. Comparison of the manufacturers’ estimated hours of use with the calculated hours of use based on a battery capacity of 130 mAh.
Thus, ideally, hearing aid manufacturers should state both current drain, expected hours of use as well as battery capacity used for the expected hours of use calculation to enable the hearing care professional to calculate what the battery consumption is likely to be. An example of a datasheet stating not only the current drain, but also the battery life and the battery capacity used for the calculations is shown in Figure 6 below.
Figure 6. Battery consumption data (battery drain, expected hours of use, and presupposed battery capacity) from the Widex D4-FS-m datasheet.
Performance on Paper vs. Real World
As we saw, a direct comparison of datasheet information across manufacturers is not readily accessible, but can be done if you are willing to do a number of calculations yourself, keeping the presupposed battery capacity constant. However, even though a direct comparison of datasheet information is possible with a little work, the ability of this information to be generalized to real life is likely to be limited, since the information has been obtained under ideal conditions.
In recent years, a variety of new hearing aids with different wireless communication abilities have become commercially available. Some are capable of exchanging coordination data, and a smaller number are also able to transmit sound to one another.
Digital transmission technology allows two binaurally fitted hearing aids to exchange data so that information about the ambient sound environment and settings from both aids is taken into account during signal processing. This exchange of data can be exploited for a number of purposes, including the preservation of localization cues and left-right synchronization of volume control adjustments and program selection. The new features rely on a continuous data exchange between two hearing aids at a rate of 5 to 21 times per second, depending on the manufacturer.
Although very useful to the wearer in many circumstances, the new features come with the cost of an increased battery drain, so when hearing aids with adaptive features and synchronization abilities are used in real life, we should expect a shorter battery life than what is stated on the datasheets.
The new digital wireless technology is also used for connectivity to external sound sources, such as a TV or a cell phone. Typically, the wireless streaming options are a major key selling point for high-end wireless digital hearing aids, since this is an important and meaningful functionality to many hearing aid wearers (Harkins & Tucker, 2007).
The streaming technologies used by the industry today differ on a number of parameters, including the delay between direct and streamed sound, the bandwidth of the streamed signal, the ability to transmit in stereo versus mono, and current drain. The streaming of TV sound, for instance, will drastically reduce the battery life in some manufacturers’ products.
The environment in which the hearing aid functions will also affect battery life. For example, hearing aids functioning with high levels of gain, in very noisy surroundings, and/or in environments with constant high-input levels will have a higher battery drain than average. Moreover, factors like humidity and temperature will also affect battery life. Another important parameter is the variation in battery capacity between different battery brands. This may also add significantly to the variation in battery life experienced in real-life use.
With the knowledge that all of these factors will influence battery life, we would not expect real-life battery consumption to be absolutely reflected in the datasheet information. But the question is how much the test mode performance reported on the datasheets will deviate from real life.
A Realistic Test of Real-World Battery Life in Current Wireless Hearing Aid Models
To provide a realistic evaluation of the battery consumption of the most recent wireless products, a benchmark study simulating real-life usage was conducted. In the study, the power consumption of the six hearing aid models listed in the introduction was tested during regular use and while streaming.
All the hearing aids were fitted binaurally to the moderately sloping N4 hearing loss of the IEC 60118-15 standard (Bisgaard, Vlaming, & Dahlquist, 2010) using the manufacturers’ standardized quick-fit options. Fittings were performed by an audiologist with solid clinical experience from her work in the Danish hospital service (Benedikte Bendtsen, MA) who was accustomed to working with products and software from different manufacturers. To make sure that the hearing aids were in a state comparable to a real-life fit, all adaptive parameters, such as feedback cancellation, were left on, and mutual data exchange was enabled.
The hearing aids were placed in a hearing aid test chamber (Interacoustics TBS25). To provide an acoustic load corresponding to the human ear and to avoid feedback during measurements, both hearing aids were connected to an occluded ear simulator (GRAS type RA0045) with no vent during the testing. Power was supplied via a battery pill connected to a battery voltage supply of 1.3V (Agilent E3610A) through a 6 Ohm resistor to provide simple battery emulation. The hearing aids were exposed to an audio file comprising the International Speech Test Signal (ISTS V1.0; Holube, I., Fredelake, S., Vlaming, M. & Kollmeier , 2007). The sound level in the test chamber was calibrated using the ISTS calibration tone to a normal speech level (65 dB SPL) using an audio analyzer (Brüel & Kjær type 2012). The audio signal was applied for 60 seconds total and current consumptions were logged. The initial 30 seconds were used to allow the hearing aids to settle. The average current consumption was measured during the remaining 30 seconds using a multimeter (Agilent U1272A).
In addition to measuring battery consumption during normal everyday use, battery consumption was also measured with audio streaming enabled to provide a realistic evaluation of the power consumption of modern wireless hearing aids during a typical TV-watching situation using a transmission device provided by the manufacturer.
A test design was used where the hearing aids were placed in a separate test chamber to avoid any extraneous sound picked up from the microphones affecting the measurement. The audio file was streamed to the hearing aids in the test chamber from the respective transmitters (i.e., Oticon ConnectLine, Phonak TVlink, ReSound Unite TV Streamer, Siemens TEK, Starkey SurfLink Media, and Widex TV-DEX ). The transmitters were placed outside the test chamber close to the hearing aids to ensure good streaming conditions; a long-range transmitter was placed at a one meter distance, and a short-range intermediate streaming device, if applicable, was placed at a 15 cm distance from the hearing aids.
The audio signal was applied to the streaming device through a mini-jack connector and adjusted so that the output level of the hearing aids during the streaming test was equal to the output level during the hearing aid sound test.
Figure 7 provides a comparison of the measured current consumption during simulated everyday use and streaming.
Figure 7. Measured current consumption of six hearing aids during simulated everyday use and streaming.
Some variation is seen across products in everyday use, ranging from 1.17 to 2.54 mA. The greatest difference between the different models’ current consumption is seen during streaming. In some manufacturers’ products, the activation of streaming has a relatively modest influence on the current consumption, while the current consumption more than doubles in others. Unexpectedly, one manufacturer’s (D) product appears to use slightly less current during streaming than in everyday use. On a purely speculative note, this could be related to the fact that this manufacturer has chosen an implementation where one of the microphones is automatically switched off during the streaming of TV sound, and consequently, maybe also part of the feedback canceling system and other subcircuits. The measured current consumption in everyday use and during streaming has been converted into battery life (hours of use) in Figure 8.
Figure 8. Battery life (hours of use) of six hearing aids during simulated everyday use and streaming based on measured current consumption. The calculations are based on an expected battery capacity of 130 mAh.
Figures 9 and 10 provide a comparison of the measured battery life during simulated everyday use and streaming to the battery life in the test mode, reported on the manufacturers’ datasheets. None of the measurement results are identical to the figures on the datasheets. Deviations of the measured current consumption to the reported current consumption on the datasheets range from 7% to 62% for everyday use. The span is even wider when streaming is activated, ranging from 2% to 74%.
Figure 9. Battery life (hours) in test mode vs. in everyday use. The battery life in everyday use is calculated from the measured current consumption. A battery capacity of 130mAh is assumed in the calculations.
Figure 10. Battery life (hours) in test mode versus when streaming is activated. The battery life during streaming is calculated from the measured current consumption. A battery capacity of 130mAh is assumed in the calculations.
There is little correlation between datasheet figures and measured real-life current consumption, even when hearing aids are used without the wireless streaming options activated. Relying on datasheet figures is difficult and, in many cases, not sufficient when answering a hearing aid wearer’s questions with regard to battery life. The standardized method used to procure datasheet figures does not capture the real-life wearer experience. Therefore, some manufacturers will indicate estimated hours of use on the datasheet, but comparing this across products requires you to do the math yourself, keeping the battery capacity constant.
Wireless functionalities seem to have a much greater impact on the current consumption than what can be deduced from the industry’s datasheets. When a hearing aid wearer chooses to activate the streaming of audio directly from a TV set to the hearing aids, for instance, it is practically impossible to rely on datasheet information to suggest the battery life under those conditions. In some devices, the activation of wireless streaming functionality will have a relatively moderate effect on battery life, while in others it will lead to a dramatic increase in current consumption.
The higher current drain and shorter battery life must be weighed carefully against the potential benefits in each patient’s case. While a high-quality wireless connection to audio sources like TV is unquestionably very desirable in itself, the variable decrease in battery life may be too high a price to pay for some patients.
As illustrated by the test results above, the impact of wireless streaming on the current consumption varies considerably among manufacturers. It is, therefore, worthwhile to ask wearers to report back on their experiences with products from different manufacturers to obtain a general overview of real life current consumption when streaming functionality is used.
Bisgaard, N., Vlaming, M. S. M. G., & Dahlquist, M. (2010). Standard audiograms for the IEC 60118-15 measurement procedure. Trends in Amplification, 14(2) 113–120.
Harkins, J., & Tucker, P. (2007). An Internet survey of individuals with hearing loss regarding assistive listening devices. Trends in Amplification, 11(2), 91-100.
Holube, I., Fredelake, S., Vlaming, M. & Kollmeier, B. (2010). Development and analysis of an international speech test signal (ISTS). International Journal of Audiology, 49, 891-903.
Kochkin, S. (2010). MarkeTrak VIII: Consumer satisfaction with hearing aids is slowly increasing. The Hearing Journal, 63(1), 19-27.
Retrieved on February 22, 2013
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Cite this content as:
Joergensen, H.S., Baekgaard, L., and Bendtsen, B. (2013, June). Battery consumption in wireless hearing aid products – Datasheet vs. real-world performance. AudiologyOnline, Article #11899. Retrieved from http://www.audiologyonline.com/