Written and maintained by CASRAI Editorial Board
Last updated
General product information only, not medical advice.
Short answer
A zinc-air battery is a primary cell that gets its power from zinc and oxygen from the surrounding air. The common hearing-aid button cell stays sealed by an adhesive tab until it is put into use. Removing the tab lets air in and starts the cell working, and it also starts the clock on its capacity. Manufacturer data shows the difference: with the tab on, a cell keeps about 95% of its initial service after one year; with the tab off, it can fall to half within 3 to 12 weeks.
Definition and scope
In a zinc-air cell, one electrode is zinc and the other is a catalysed carbon cathode that takes in oxygen from the air through a small hole in the casing. This page covers the miniature button cells used in behind-the-ear and in-the-ear hearing aids. Larger and rechargeable zinc-air designs exist but are outside its scope.
Energizer’s application manual describes the miniature zinc-air cell as designed primarily to power hearing aids, with the highest capacity-to-volume ratio among miniature batteries, a relatively flat discharge curve and a nominal voltage of 1.4 V. It states that its cells contain no added mercury. That is a statement about that maker’s cells, not about every brand.
How the tab and air hole work
What happens inside the cell
The manual lists the construction as a gelled zinc powder anode, a catalysed carbon cathode, a potassium hydroxide (KOH) solution in water as the electrolyte, a separator, a molded nylon gasket and a nickel exterior. The reactions it gives are:
- Anode: Zn + 2OH– to ZnO + H2O + 2e–
- Cathode: O2 + 2H2O + 4e– to 4OH–
- Overall: 2Zn + O2 to 2ZnO
The manual states that the cell must have access to air (oxygen) to operate.
Why the tab matters
The manual says the cell is activated by removing the adhesive-backed tab from the air access hole, and that excessive moisture transport can degrade performance, so the hole is sealed until use. It calls the tab seal the key to shelf life. Its figures for cells stored at room temperature with the tab on are 95% of initial service after one year and 90% after two years, with accelerated testing indicating more than 85% at three years.
| Condition (Energizer, 2004 manual) | Stated result |
|---|---|
| Tab on, room temperature, 1 year | 95% of initial service |
| Tab on, room temperature, 2 years | 90% of initial service |
| Tab on, accelerated testing, 3 years | Should exceed 85% |
| Tab off, 20 °C (68 °F) | Fresh capacity maintenance of 50% after 3 to 12 weeks, depending on size |
| Tab off, beyond 20 weeks, 20 °C | 0 to 10% |
The manual adds that continuous-use temperature runs from -10 °C to 55 °C, that the cells suit high-to-medium drain uses that consume capacity within a few weeks of opening the seal, and that storing a cell overnight in a hearing-aid drying device has a negligible effect on service life. It also notes that individual battery characteristics are sometimes modified, so the maker’s current information governs.
Types and related cells
Hearing-aid zinc-air cells come in several physical sizes. A hearing-care provider guide (Beltone) lists the sizes and colour-coded packaging as 5 (red), 10 (yellow), 13 (orange), 312 (brown) and 675 (blue). This page does not map those labels to formal standard designations. Supply lists such as the audiology clinic supply checklist name these sizes as stock items.
Zinc-air chemistry is also researched in rechargeable and larger formats. Those formats are outside the scope of this page. For background on the underlying chemistry of metals and oxides, see what is inorganic chemistry, and for the electrolyte, what is an aqueous solution.
Where it matters for clinics and supply rooms
Handling: the tab starts the clock
Because opening the seal begins capacity loss, the manual itself advises keeping the tab seal in place until the cell is used. Cells already unsealed lose capacity in weeks, not years.
Safety: small cells are still a swallowing hazard
NHS England and NHS Improvement issued National Patient Safety Alert NatPSA/2019/003/NHSPS on 13 December 2019, titled “Risk of harm to babies and children from coin/button batteries in hearing aids and other hearing devices.” It states that while larger lithium batteries have the greatest potential to cause harm, “the smaller zinc-air batteries, used in hearing aids, cochlear implants, bone-anchored hearing aids (BAHA) and similar equipment, still present a significant risk.” Children under five are most at risk, because a battery can lodge in the narrow oesophagus and cause rapid tissue damage.
The alert was prompted by a one-year-old who swallowed a battery from a hearing aid without a secure battery compartment. For organisations supplying NHS-funded hearing aids in England it required, by 11 September 2020:
- secure battery compartments on all hearing devices for children under five, and consideration of them for people living with under-fives or with additional risk factors;
- a review of purchasing and supply so audiology teams can reach devices with secure compartments;
- information for parents and users on ingestion risk and safe storage of spare and used batteries for recycling.
The alert reported 13 ingestion-related incidents between 7 July 2016 and 8 July 2019, with three children needing critical care, and cited the Child Accident Prevention Trust’s estimate of around two child deaths a year in the UK from coin and button battery ingestion. These figures are UK-specific and come from the alert. It refers to IEC 60601-2-66:2015 as a manufacturer standard for hearing aids. Outside the UK, follow the rules and guidance that apply where you work.
Common misunderstandings
- “A fresh cell should work at full strength the instant the tab comes off.” The cell needs air to reach full output. Energizer advises airing for 30 seconds before placing the cell in the device for maximum power; a hearing-care provider (Beltone) tells users to wait a full minute. Those are two owners giving two figures, so follow the instruction on the packaging in front of you.
- “Unused cells keep forever once opened.” They do not. Capacity falls quickly after the seal is removed, as the table above shows.
- “No added mercury applies to every zinc-air cell.” Energizer states it for its own cells. Beltone says most makers now sell zero-mercury versions. Check the packaging or the maker’s data for the brand you stock.
- “A cell that seems weak is faulty.” Hearing-aid circuits can misbehave when a cell sags below roughly 1.05 to 1.1 V (AudiologyOnline), well under the 1.4 V nominal figure, and sweat or humidity can shorten life. Service life is cell capacity divided by the current the device draws.
FAQ
How long should a zinc-air battery air before use?
Energizer’s application manual says to allow 30 seconds before placing the cell in the device for maximum power. Beltone advises a full minute. Follow the instruction printed on your cell’s packaging.
Why does the tab matter?
It seals the air hole. With it on, Energizer reports about 95% of initial service after one year; with it off, a cell may keep only half its capacity after 3 to 12 weeks at 20 °C.
Are zinc-air button cells dangerous if swallowed?
NHS England’s 2019 alert says zinc-air cells in hearing devices still present a significant risk, especially to children under five, because a swallowed battery can lodge in the narrow oesophagus. It asks suppliers to give users information on the ingestion risk and to provide secure battery compartments on devices for children under five.
Where do disposal and storage rules come from?
The NHS alert asks that spare and used batteries awaiting recycling be stored safely, away from young children. Hearing-care guidance also advises keeping cells at room temperature and away from heat, humidity and loose metal objects.
Sources
- Energizer, “Zinc Air (Zn/O2) Application Manual” (2004), data.energizer.com/pdfs/zincair_appman.pdf, checked 30 October 2026.
- NHS England and NHS Improvement, National Patient Safety Alert NatPSA/2019/003/NHSPS, 13 December 2019, england.nhs.uk alert PDF, checked 30 October 2026.
- Beltone, “Your guide to hearing aid batteries,” beltone.com, checked 30 October 2026 (provider guidance; used for the one-minute wait, size colours and storage).
- AudiologyOnline, “Power to Hear, Powered by 1174,” audiologyonline.com, checked 30 October 2026 (device voltage behaviour).
