The vast majority of modern hearing aids use disposable zinc-air batteries. Typical battery life depends on how long the aid is worn each day, as well as the amount of sound the hearing aid must put out (greater hearing loss requires greater hearing aid volume and shortens battery life). A general rule of thumb is that batteries will last approximately 7-10 days. Changing the batteries is the most common maintenance activity hearing aids require.
There is a substantial difference between replacing the battery in a child's hearing aid and an adult's hearing aid. Just as audiologists will often disable any physical buttons or switches on a child's hearing aid to avoid accidental changes, pediatric hearing aids feature child locks on the battery doors. Additionally, hearing aid batteries are toxic if swallowed, so safety locks also keep the batteries out of the hands of children. Figure 1 shows one type of battery door safety lock, but these systems can differ by manufacturer. Hearing aid manuals are typically available online in PDF format, so if you experience difficulty with a safety lock, help is only a few mouseclicks away.
Changing the battery on an adult's hearing aid is substantially easier. The battery door is simply pulled opened and the battery freely comes out.
A common theme in both pediatric and adult hearing aid batteries is that they must be inserted in the proper orientation (facing the correct direction). If the battery is facing the wrong way, the hearing aid will not work. Note the green-highlighted plus sign on the battery in the animation. Most often, hearing aid battery compartments will have a small plus sign (as in the animation) indicating how to insert the battery. Because the aid will not function unless the battery is correctly oriented, some hearing aids have battery compartments that are specifically designed to fit the battery in only one direction. A backwards battery will simply not fit, and serves as an indication that it is not oriented properly. Other hearing aids, however, have no such protection, so care must always be taken to ensure the hearing aid is powered on. Two such tests are the feedback test and the listening check.