A battery is a chemical reaction put on pause in a can. Closing the circuit restarts it, and it stops when one of its two ingredients runs out.
Single-use or rechargeable
A primary cell, what most people call a battery, empties once. A rechargeable battery (an accumulator) recharges hundreds of times. Rechargeables have their own sheet: Les batteries.
Inside a cell, two different materials with an electrolyte between them. One gives up electrons, the other takes them: the electrons go round through the outside circuit, and that current is what we use. The principle is so simple you can make one with two metals and vinegar, see Making a battery.
The families
| Type | Voltage | Strengths | Weaknesses |
|---|---|---|---|
| Zinc-carbon ("heavy duty") | 1.5 V | Very cheap | Low capacity, leaks easily |
| Alkaline | 1.5 V | The standard, good capacity at low drain | Loses a lot under heavy drain and in the cold, can leak |
| 1.5 V lithium (AA, AAA sizes) | 1.5 V | Light, works down to −40 °C, keeps 20 years | More expensive |
| 3 V lithium (CR2032, CR123A) | 3 V | Long life; watches, car keys, tactical torches | Different voltage: doesn't replace two 1.5 V cells just anywhere |
| Silver oxide (button cells) | 1.55 V | Very steady voltage, watches | Small capacity |
| Zinc-air (hearing aids) | 1.4 V | Huge capacity for its size | Activated by pulling off the sticker, spent within weeks after that |
Sizes
| Common name | IEC designation | Size |
|---|---|---|
| AAA | LR03 | 10.5 × 44.5 mm |
| AA | LR6 | 14.5 × 50.5 mm |
| C | LR14 | 26.2 × 50 mm |
| D | LR20 | 34.2 × 61.5 mm |
| 9 V | 6LR61 | six small cells in series in one case |
Capacity isn't fixed. An alkaline AA gives about 2,500 to 3,000 mAh in a clock or a remote, but less than half that in a hungry device like a camera flash or a motorised toy. For those uses, lithium cells or rechargeables do far better.
Storing batteries
- How long: 5 to 10 years for alkaline, 10 to 20 years for lithium, in good conditions. The expiry date is printed on the cell.
- Where: cool, dry, at a steady temperature. The fridge adds almost nothing for modern alkalines, and condensation when you take them out can harm them.
- How: in their packaging or a box, terminals protected. A loose 9 V battery in a drawer can touch a metal object, heat up and start a fire.
- Not in stored devices: an alkaline forgotten in a torch will eventually leak and eat the contacts.
Tips from people who use a lot of them
- The white crust on a leaking alkaline is potassium hydroxide, a corrosive base. Clean it with a cotton bud dipped in vinegar or lemon juice (the acid neutralises the base), then rub the contacts with an eraser or a fine file. Gloves and glasses if there's a lot.
- The bounce test: dropped upright onto a hard table from about ten centimetres, a fresh alkaline lands with a dull thud, a spent one bounces. It's approximate, but real: as it discharges, the inside of the cell changes consistency.
- Never mix new and used cells, or two brands or types in the same device: the weakest gets "reversed" by the others and leaks.
- Recharging an ordinary alkaline is not advised: it heats, leaks or swells. To recharge, use low self-discharge NiMH cells (1.2 V): they keep most of their charge for years and replace alkalines almost everywhere.
- Cold drains an alkaline: keep spare batteries in an inside pocket, and warm a cold one against your body before deciding it's dead.
- A button battery swallowed by a child is an absolute emergency. Within a few hours it burns the oesophagus. Go straight to the emergency room, don't make the child vomit. Keep them out of reach, and the same goes for remotes whose battery cover opens easily.
Used batteries go back to the shop for recycling: they contain metals that can be recovered.