Storing spare coin cells: shelf life, heat and loose cells
A sealed coin cell can sit for years and still work. A loose one in the junk drawer is a short circuit, and a child safety problem, waiting to happen.
Keep spare coin cells sealed in their original retail packaging, in a cool, dry place at normal room temperature, out of sight and reach of children. Energizer rates its lithium coin cells for a 10 year shelf life under those conditions. Do not refrigerate them, and never let loose cells sit with keys, coins or each other.
How long do coin cell batteries last in storage?
Longer than most batteries. Energizer's lithium coin handbook puts the shelf life of its lithium coin cells, stored at normal room temperature and humidity, at 10 years, and says they lose about 1 percent of their capacity a year through the seal. Its CR2032 datasheet lists the same figure: self discharge of about 1 percent a year. Panasonic's lithium battery catalogue makes a similar claim for its coin cells: kept in proper conditions, 90 percent of capacity remains after ten years.
Two oddities of old stock are normal. Energizer notes that cells stored for years in a sealed pack can give off a faint ether-like smell of the electrolyte solvent when the pack is first opened, and says it is not a safety concern. Long storage can also build a thin resistive layer on the lithium, so an old cell may sag slightly when first loaded. Once it is working, Energizer says, the layer thins and internal resistance typically returns to normal.
Those figures describe a maker's own sealed cells. A loose cell of unknown age tells you nothing, which is one more reason to keep the packet. Our guide to coin cell markings explains why the date usually lives there and not on the cell.
What temperature should you store batteries at?
Normal room temperature, somewhere dry. Neither Energizer nor Duracell gives a precise number in its consumer advice, but both agree on the essentials.
| Condition | What the makers say | Source |
|---|---|---|
| Room temperature, dry | The recommended place for spares | Energizer battery care, Duracell FAQ |
| Hot places | Do not store there: elevated temperatures can cause capacity loss, leakage or rupture | Energizer battery care |
| Refrigerator | Not necessary (Energizer); not necessary or recommended (Duracell) | Energizer battery care, Duracell FAQ |
| Original packaging | Keep spares in it until ready to use | Energizer, Duracell, Energizer safety data sheet |
| Loose with metal objects | Can short circuit, leading to heat, leakage or rupture | Energizer battery care, Duracell FAQ |
So skip the fridge door, the glovebox and the shelf above the radiator. Energizer's safety data sheet for its coin cells repeats the point in trade language: store in a cool, well ventilated area, because elevated temperatures shorten battery life.
Why should loose batteries not share a drawer?
Because a coin cell is all terminal. Its two flat metal faces are its contacts, so a key, a coin or a paper clip lying across both closes the circuit. Energizer's battery care page warns against carrying loose batteries with metal objects like coins and paper clips, because this can short-circuit the battery, leading to high heat or leakage. Duracell's FAQ says the same: loose batteries can be shorted by contact with metal objects and leak or rupture.
Cells can do it to each other, too. Energizer's coin cell safety data sheet lists "jumbled batteries in bulk containers" first among sources of short circuits. A short of a few seconds will not seriously affect a cell, the sheet says, but a prolonged one drains it, generates significant heat and can open the safety vent. A tub of mixed spares is exactly that jumble.
The fix is boring. Keep spares in the original retail pack, which Energizer recommends specifically to prevent short-circuiting. If a cell is already loose, Energizer suggests a strip of insulated tape across its contacts, or an individual case or bag, to keep it away from coins, keys and jewelry.
Where should you keep spare button batteries away from children?
Out of sight, not just out of reach. National Capital Poison Center's button battery safety tips say never to leave batteries sitting out, and to store spare batteries, and batteries waiting to be recycled, out of sight and reach of young children. The same page adds a list of places not to use: near pills or in pill bottles, on bedside tables, loose in a pocket or purse, and anywhere they could be mistaken for food.
The cells it singles out are the ones most people stockpile: anything as big as a penny or larger, often stamped CR2032, CR2025 or CR2016. Energizer prints the same warning on its CR2032 datasheet, "KEEP OUT OF REACH OF CHILDREN", and its safety data sheet adds a plain instruction: keep in original package until ready to use, and dispose of used batteries immediately.
A junk drawer fails on every count: it is loose, it is reachable, and it is full of metal. Why ingestion is so dangerous, and what to do if it happens, is covered in our button battery child safety guide.
What about dead cells waiting for recycling?
Treat them like spares. Poison Control says dead or spent batteries still have enough energy to cause serious damage, and advises taping button batteries all the way around, twice, before disposing of them. It notes the tape does not affect recycling. Until then they belong in the same high, closed place as the fresh ones.