Headlamp and batteries: choosing, storing, using in the cold

Modern headlamps make light with light-emitting diodes (LEDs), which turn a little electricity into a lot of light. Brightness is often given in lumens – the total amount of light the lamp gives off. More lumens sounds good but also uses more energy. For reading a map, cooking or walking on a known path a low or medium mode is usually enough.

Light is a matter of energy over time. A battery holds a certain amount of energy, and the lamp divides it up: lots of light for a short time or little light for a long time. A useful low mode can last many times longer than the highest one. Many lamps also automatically turn the brightness down after a while so they do not get too hot or to spare the battery.

Cold slows the chemical processes in batteries. The energy is still there, but it is harder to draw out – the lamp gets dimmer or seems to run flat. When the battery warms up again, some of the performance returns. That is why in frost you carry the lamp and spare batteries close to your body and put them in your sleeping bag at night.

Roughly, there are three groups. Alkaline batteries are available everywhere but lose a lot of performance in the cold and can leak during long storage in a device. Lithium primary batteries are lighter, usually work better in the cold and store for a long time – whether your lamp tolerates them is stated in the manual. Rechargeable batteries save waste and money over time but need regular recharging, because they slowly discharge even when unused.

Many lamps have a built-in battery that you charge with a cable. That is convenient as long as there is power. During a longer power cut or on a multi-day trip you then need a power bank or another way to charge. For emergency preparedness, a lamp that can also take ordinary batteries is practical.

Lithium rechargeables like neither heat nor damage. Many manufacturers also advise against charging them in freezing conditions. For storage, some manufacturers recommend keeping rechargeables partly charged rather than completely full or empty. Store single-use batteries cool and dry and keep an eye on the expiry date.

Do not look only at the highest lumen figure but at how long the lamp lasts in low and medium modes. Figures according to the ANSI/PLATO FL 1 standard make lamps easier to compare, because all manufacturers then measure the same way. The standard does not say, however, whether a lamp suits your purpose.

In practice what matters is: simple operation that works with gloves and when half asleep; a very low mode or red light; protection against rain; a comfortable headband; and a lock against switching on by accident. Without a lock the lamp can switch on in the pack and drain unnoticed. If it has no lock, you can carry one battery reversed or separately.

Red light has a special advantage: your eyes slowly adapt to the little light there is in the dark, and that takes many minutes. Bright white light quickly undoes this adaptation, while dim red light disturbs it less. You also dazzle others in the tent or group less.

Stop using lithium batteries and power banks that are damaged, swollen or have become very hot, and charge them only with suitable chargers. Special rules apply to spare batteries and power banks on flights – ask the airline beforehand.

Button cells and small batteries are dangerous for small children if swallowed. Keep them out of children's reach. If you suspect a child has swallowed a battery, seek medical help immediately or call the local emergency number (112 in the EU) – do not wait to see whether symptoms appear.

Civil protection authorities recommend torches or headlamps rather than candles for power cuts, because open flames can start fires. Keep a lamp for each person in the household in a fixed place everyone knows, so it can be found quickly in the dark.

Test lamps and batteries twice a year, for example at the start of summer and of winter. Switch on every mode once, check the contacts for white or greenish deposits (corrosion) and recharge rechargeables. Take empty batteries to the proper collection points, not into household waste.

If you rarely use a lamp, store alkaline batteries separately next to it rather than inside – that way a leak cannot damage the lamp. Get to know the controls in the dark: how do you go straight to the lowest mode? How do you lock the lamp? If you practise this at home, you will manage it in an emergency even with cold fingers.