Article
Feb 2006
Hearing aid Battery Life
How long will my hearing aid batteries last?
I bet you wish you had a dollar for every time you heard that
question. So, what do you tell your patients when they want to know? Do
you look at a chart, or take an educated guess? Just how can you tell how
long a hearing aid battery will last anyway?
And even more importantly, what do you tell your patients that complain
that their hearing aid batteries don’t last long enough? How can you
verify there is indeed a problem, or that maybe the patient has
unrealistic expectations.
Thankfully, there is an easy way to tell how long hearing aid batteries
will last in any hearing aid, but first you need to understand a little
about how hearing aids work with different types of batteries.
If you are in a hurry you can download our guide to measuring battery
life here.
The common factor in all hearing aids:
Whether you are working with an older linear hearing aid, a brand new
digital instrument, or anything in-between, there is one common element.
They all get their power to function from a hearing aid battery. Every
electronic circuit needs some sort of power or energy source to operate –
and for hearing aids, it is of course the battery. Now, when you turn the
hearing aid ON, it uses the energy stored in the battery. Hearing aids
need a certain amount of energy in order to operate, and the circuit will
continue to operate until the stored energy in the battery is not
sufficient to operate that hearing aid circuit any longer.
If you want an uncomplicated analogy, think of a hearing aid as your
car, and the battery as a tank of gas. You start off with a full tank, but
as you drive around town the gas in the tank is used for energy to run the
car, and once the tank is empty the car stops. You’ve run out of gas, just
like a hearing aid battery runs out of energy to operate a hearing aid.
There are factors which impact how far you can drive on a tank of gas.
How economical the car is, the size of the gas tank, if you leave your car
parked with the motor running. The same is true for hearing aids. Some low
amplification circuits use less energy, while some high gain – high power
circuits use a lot more. The size of the battery matters too, as this
directly correlates to how much energy can be stored in the battery. And
of course if you leave the hearing aid ON while it sits on the dresser
overnight you will waist battery life. We’ll talk more about the energy
stored in the battery in a minute.
So how can you tell how long the hearing aid battery will last?
First, we need to measure what is commonly referred to as Battery
Drain. It is actually the amount of electronic current the hearing aid
needs to function, and it can easily be measured using a battery drain
meter. The drain meter typically plugs into the hearing aid through the
battery compartment using a special connector called a battery pill, or
battery sub. If you’ve never seen one you can view here:
http://www.lightningenterprises.com/bdm.html
To get an accurate reading from the drain meter, you must first turn
the hearing aid ON and adjust the volume control of the hearing aid (if it
has one) to approximate user level. Then simply plug the hearing aid into
the drain meter and read the result on the display. Make sure the hearing
aid is not whistling or feeding back. This can cause some hearing aid
circuits to use more power, and therefore skew your measurement. Plug the
sound outlet port if necessary to keep the hearing aid from feeding
back during measurement.
What is this Battery Drain Reading Mean?
The number you see on the display is the amount of electronic current
the hearing aid is using to function. It is displayed in milliamps, or
1000ths of an ampere if you want to get technical. And, this is the
mystical number you will us to calculate how long your customer’s hearing
aid battery will last.
One more factor
Size matters when it comes to hearing aid batteries. Just like the gas
tank in your car, the larger the tank, the further you can drive before
filling up. A size 13 battery stores more energy than a size 312, which
stores more energy than a size 10A. So, this is going to be a factor in
calculating how long the battery will last in a hearing aid. This stored
energy has a value called milliamp hours. And though this value may differ
depending on battery manufacturer, there are some default values you can
use for your calculation. You can also get the milliamp hours from the
battery packaging.
Here are the default values depending on battery size:
| Battery Size: |
Milliamp Hours: |
| 675 |
600 mah |
| 13 |
260 mah |
| 312 |
130 mha |
| 10A |
70 mah |
| 5A |
35 mah |
The Calculation
Now we have all the information we need to determine how long your
customer’s hearing aid batteries will last. Divide the Battery Capacity in
milliamp hours (determined by the battery size) by the Battery Drain of
the hearing aid. This will give you the approximate total number of hours
the hearing aid battery should last in that particular hearing aid. Next,
divide the total number of hours by the number of hours the user will wear
the hearing aid during the day.
Example: You want to calculate how many days a battery will last in an
ITE instrument using a 312 size battery. You have measured the Battery
Drain at .75 ma and we will use the default Battery Capacity from the
table above which is 130 mah. We will assume the user is wearing the
hearing aid 16 hours per day.
Total Hours (TH) = Battery Capacity (BC) / Battery Drain of Hearing Aid
(BD) =
130 / .75 = 173.33 Total Hours.
Total Days (TD) = Total Hours (TH) / Hours worn per day (HW) =
173.33 / 16 = 10.83 Days.
About the Author
Chris Perkins is the owner of Lightning Enterprises, and facilitates
the Lightning Enterprises newsletter. He has worked in the hearing aid
industry since 1991 in hearing aid manufacturing and product development,
as well as equipment and process consulting.
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