Batteries in the things you hardly ever use

Everything here earned its place by changing an outcome. Nothing about batteries in occasional-use equipment is included to round the number up.

Why occasional use is the hardest case

Equipment used daily keeps its battery within a working range, and the owner notices immediately when capacity falls. Equipment used twice a year sits at whatever charge it was left at, for months, at whatever temperature the cupboard is.

The failure is discovered at the moment the equipment is needed, which is usually the least convenient possible time. Torches, emergency equipment, seasonal tools and smoke alarms all follow this pattern with great regularity. Planning for it is straightforward and requires deciding on a chemistry and a checking habit rather than any special skill.

Alkaline cells and leakage

Alkaline cells produce hydrogen gas as they age and discharge, and eventually the seal vents caustic electrolyte. The electrolyte corrodes contacts, tracks along circuit boards and destroys equipment that was otherwise perfectly good.

Leakage is most likely in cells left installed and fully or partly discharged for a long period. Mixing old and new cells, or different brands, increases the chance by driving one cell into reversal. Removing cells from anything being put away is the single most effective preventive measure available.

Lithium primary and rechargeable cells

Lithium primary cells have very low self-discharge and wide temperature tolerance, which suits equipment left for years. They cost more per cell and are worth it specifically in items that are rarely used and expensive to have fail.

Rechargeable lithium cells lose capacity through calendar ageing regardless of use, and heat accelerates it markedly. Leaving a rechargeable pack fully discharged risks the protection circuit locking it out permanently. Low self-discharge nickel metal hydride cells hold charge far better than older rechargeables and suit intermittent use well.

Equipment that must work when needed

Smoke and carbon monoxide alarms have specified battery types and, on sealed units, a stated end-of-life date for the whole device. Emergency lighting and backup power need periodic testing rather than periodic inspection, since a battery can look fine and deliver nothing. Uninterruptible power supplies have batteries with a service life of a few years and often fail without any indication.

In the small print, vehicle and equipment starter batteries deteriorate when left discharged and benefit from a maintenance charger during idle periods. For anything safety-related, following the manufacturer's testing schedule matters more than any general advice.

A workable routine

Choose a checking date tied to something memorable, such as a clock change or a season, and check everything then. Remove cells from seasonal equipment when it goes away, and store them separately in a cool place. Label packs and devices with the date the cell was installed, since capacity questions become answerable once you know the age.

Keep a small stock of the sizes you use and rotate it, since cells in a drawer also age. Test rather than inspect, because a cell at rest voltage can still be incapable of delivering current under load.

Disposal and safety

Damaged, swollen or leaking cells should be handled carefully and taken to appropriate collection points rather than general waste. Lithium cells present a fire risk when damaged or short-circuited, and taping terminals before disposal is standard advice. Rules on battery disposal vary between countries, and most have collection schemes at retailers or civic sites.

Judged against the category, charging damaged or swollen packs is unsafe and should not be attempted regardless of how convenient it would be. This site does not offer safety guidance beyond the general, and manufacturer instructions and local waste authorities are the correct sources.

Everything above, in order of what to do first

1. Why occasional use is the hardest case. Equipment used daily keeps its battery within a working range, and the owner notices immediately when capacity falls.
2. Alkaline cells and leakage. Alkaline cells produce hydrogen gas as they age and discharge, and eventually the seal vents caustic electrolyte.
3. Lithium primary and rechargeable cells. Lithium primary cells have very low self-discharge and wide temperature tolerance, which suits equipment left for years.
4. Equipment that must work when needed. Smoke and carbon monoxide alarms have specified battery types and, on sealed units, a stated end-of-life date for the whole device.
5. A workable routine. Choose a checking date tied to something memorable, such as a clock change or a season, and check everything then.
6. Disposal and safety. Damaged, swollen or leaking cells should be handled carefully and taken to appropriate collection points rather than general waste.

The takeaway

Take the cells out of anything going into a cupboard, and give yourself a date to check the rest.

The question is rarely which is best. It is which is enough.