Sizes:  Hearing aid batteries come in four sizes - 675, 13, 312, and 10* with 675 being the largest and 10 the smallest.  Over the last 20 years, all hearing aids have been designed to accommodate these four sizes. 

     Many companies manufacture hearing aids batteries including Rayovac, Duracell, Eveready, and Varta to mention a few.  All use the same color coding system to differentiate the four sizes of batteries:  BLUE for 675; ORANGE for 13, BROWN for 312 and YELLOW for 10.  So no matter what brand you buy, you can find the battery size you need by knowing what COLOR you take.

*There exists one size smaller (5), that has not been very popular due to the extremely limited battery life. http://www.caohc.org/publications/meter.php

     Behind the ear (BTE) style hearing aids usually take either a 675 or 13, since they are larger.  In-the-ear (ITE) usually take a 13 size; in-the-canal (ITC) the 312 size and completely-in-canal (CIC) the 10 size. 

Capacity.  Each hearing aid battery cell comes with a certain amount of battery life, referred to capacity.  The larger the battery size, the higher the capacity when tested at the same current drain of 1.0 milli-amperes per hour (mAh).   In the table above, notice the hours of battery life under each battery size.  This represents the number of hours a typical battery would last if the hearing aid's current drain were exactly 1.0 milli-amperes.  While hearing aid batteries may look like watch batteries, batteries for hearing aids do not last very long at all when compared to watch batteries due to the unusually high current drain

      So the answer to the question, "HOW MANY DAYS WILL MY HEARING AID BATTERY LAST?" is primarily dependent upon what battery SIZE you take and the CURRENT DRAIN of your hearing aid.   

Variables affecting use:  Typically, the "current drain" is noted on the specification sheet for each hearing aid.  You might have to ask your audiologist for that information.  Smaller, lower gain hearing aids tend to have lower current drain, typically between 1.0 - 1.5 milliamperes per hour (mAh).  Very strong, high powered BTE's might drain at 3.0 -5.0 mAh. 

     So let's try a calculation.  If the drain on a 13 battery were 1.5mAh, how many hours of life would you get?  Let's figure it out.  You would divide 290 hours (shown above for 13 batteries) by 1.5mAh (the current drain).  As such, battery life should be around 193 hours. 

     So how many days is that?  That depends upon the average number of hours you use your hearing aid each day. Most people wear their hearing aids approximately 10-12 hours per day.  In the example above, that would be 16-19 days.  However, if you use the hearing aid(s) only five hours per day, you should more days, right?

     Are there other variables?  Yes, a few.  Other variables affecting battery life include:

• Occasionally, the level of volume and/or level of input noise; but this is only true for high-gain instruments.

• Altitude, due to the catalyst being "air" as described below.  This is not often a problem for most people in the U.S., but is a problem for those of us in Colorado who live at 5000 feet and above.  Patients report getting an extra one or two days when traveling to low altitude areas.  This is the reason.

Materials.  Hearing aid battery cells are called "zinc-air" as it relates to its material contents.  This is why you often see an "A" following the number, such as  675A or 13A, etc.  Batteries have a positive (+) and negative (-) side and must be inserted into the hearing aid's battery compartment correctly.  One side of the battery contains mercury and the other zinc.  To make the battery operational, there must be a catalyst; in this case the catalyst is air (yes, air!).

 The air catalyst is activated by removing a protective seal covering two holes on the battery (shown on the picture).  Once the holes are exposed, the battery begins discharging.  As noted, batteries include mercury.  Mercury is environmentally hazardous, but don't worry, the amount included is so extremely marginal that no ill effect can occur to you or the environment.  You just throw it away.