Many markets are moving to mercury-free zinc air batteries for hearing aids. Although more environmentally friendly, the new battery technology is not a great friend to hearing aid performance. In a test of Rayovac brand batteries, the first generation of mercury-free were found to perform significantly worse than batteries with mercury. However, the newest mercury-free battery technology from this manufacturer comes closer to previous battery performance. It is recommended that this generation of mercury-free batteries be used for GN hearing instruments. These batteries have an expiration date of 2015 and later.
The graph below shows how the battery voltage drops over time as a high load is applied (the red curve shows the load current). The blue curve is the performance for Rayovac with mercury, the pink is their first generation mercury-free, and the green is their latest generation mercury free.
Did You Know?
In GN wireless hearing instruments, the exit from streaming due to low battery and the low battery warning prior to hearing instrument shutdown operate on different principles. This is due to different demands to the battery performance:
- The low battery warning is triggered by a steady fall in voltage. When the averaged voltage drops below a nominal level for at least 30 seconds, the warning is triggered and will continue every 5 minutes until device shutdown.
- The wireless exit is triggered by successive dips in voltage below a nominal level over a very short time period. When streaming, the wireless trans¬mission is characterized by power pulses. The battery must be able to withstand the resulting momentary dips in voltage.