Do hearing aids work normally when the battery is low?

This is a very good question and one that my patients frequently ask. The quick answer is no, meaning they may malfunction on a low battery. However, the period of time the battery is low is extremely small - probably a couple of hours at the very most, depending on the type of battery used. The battery current demands from todays advanced hearing aids that are designed to do a vast variety of things, from directionality and noise management to wireless streaming and ear to ear communication (device on one ear to device on the other ear) are so huge that there has to be a steady delivery of current from the battery. There may be disruption of some of these high level functions the hearing aids perform on a lower voltage. Todays batteries are designed to deliver steady performance throughout the life of the battery and when the battery life is over it dies very quickly. Also, with the advent of rechargeable batteries such as the silver zinc battery from Z-Power and especially the lithium-ion rechargeable hearing aid technology from Phonak, there have been huge strides in this aspect of hearing aids. There may be other rechargeable technologies that I have failed to mention too. Please note that my commnets are purely from my own observations in my practice over the past 35 years and not from research.

Hearing aids for many years, since the advent of Zinc Air batteries inthe 1980s, have been designed to maximize performance for as long as possible before "dying."  The reason for this is so that the aids perform well throughout the battery life, rather than degrading over time where it would be better to visit grandma at the beginning of the week rather than at the end of the week.  With a steady performance, you can visit grandma any time and expect good performance from the hearing aids (as the relate to the batteries).

At a certain point, battery performance begins to decline, and it is very precipetous and quick how it happens.  So the battery goes dead all at once, but only after performing at maximum throughout its use.  There is a small "in-between" time where the voltage decreases and performance becomes questionable, with side effects like intermittency or "motor-boating" sounds.  This period is usually very short (15 - 90 minutes).  Manufacturers about 15 years ago capitalized on this, designing the hearing aids to detect this voltage decrease and react by sending indicator tones ("Low battery indicators") to let the user know that the batteries would be going dead soon (usually 15 - 60 minutes after the first time the indicator tone is heard).  This is not a very standard feature in most hearing aids, so you can assume that until you hear the low battery indicator the hearing aids are functioning at optimum, but after the indicator tone the aids might not function as well.

Proper storage of batteries is very important also, to maximize battery life.  They should be kept in a warm, dry area; the stickers on the backs of the batteries actually act as a seal.  Once the seal is broken, the battery is activated and can't be deactivated.  There is a myth that if you keep the batteries in a refrigerator it extends their life, but this is actually very bad for batteries, as the moisture in this environment can cause the sticker adhesive to fail, activating the battery prematurely.  The user then might later remove the sticker, only to find that the battery is already dead since the seal was broken.  The same can happen if the batteries are otherwise kept in a kitchen or bathroom.  A good rule of thumb is that if the room has a sink, don't store the batteries in that room.

Today's digital technology and current battery manufacturing processes allow virtually exact power from beginning to end. The aids will perform equally from "hot' battery to the end of it's life. However, when the battery voltage drops enough to signal the aid to send an alert tone, the user has limited time for replacement before the battery is no longer functional. Based on my own usage, my aids perform at the same level until completely drained. Once I hear the alert, I usually have less than 30 minutes to replace the batteries.  

Hearing aid batteries often lose power very suddenly, so for the most part the aid should function normally. However, if the hearing aid sounds distorted or you find yourself turning the hearing aid up it could be a good indicator to change the hearing aid battery. Most hearing aids will be when the battery is low. We often tell our patient to change the batteries out at the same time if there is indication the batteries are dead or going low.

Dear;

Theoretically it should.  The hearing aid circuitry is normally design to keep the charge constant until the battery goes below a cetaitn voltage, i.e. 1.2 V in most cases, then the circuit will shut the hearing aid off.  That ways, the hearing aid will function at the designed level all the way until the battery is no longer capable of supporting the normal function of the hearing aid circuitrry.  The cut off point is varied from design to design, i.e. manufacturer to manufacturer.  But again, in theory it should.

Hope this helps