Light and Charge in the Cold

Batteries work by chemical reactions, and cold slows those reactions down. In a lithium-ion cell the electrolyte becomes more resistant, so the battery cannot deliver current as easily. Your device sees voltage drop under load, decides the battery is nearly empty and shuts down. Bring it back to room temperature and much of the "lost" charge reappears.

Charging is a different matter. Most lithium-ion manufacturers specify a charging range starting at around 0 °C, because charging a very cold cell can cause lithium plating — a form of permanent damage that reduces capacity and, in rare cases, affects safety. Many modern devices refuse to charge when too cold. That is a protection feature, not a fault, and it is worth respecting: warm a power bank and phone inside your jacket or sleeping bag before connecting them.

Disposable lithium primary cells (AA and AAA lithium iron disulfide) generally handle deep cold much better than alkaline cells, which is why many winter travellers keep a set in a backup headlamp. They cost more, and a few devices are not rated for their slightly higher fresh voltage, so check the manual.

In Tromsø the sun does not rise for roughly two months each winter; in Kiruna and Rovaniemi, daylight in December lasts only a few hours. A dependable headlamp is not optional. Many manufacturers rate lights using the ANSI/PLATO FL1 standard, which defines how lumens, beam distance, runtime and impact resistance are measured. It is a useful common language — with caveats.

FL1 runtime is measured until output drops to 10% of the initial level. A lamp might claim "200 lumens, 40 hours" while spending most of those hours far dimmer than 200 lumens. Tests are also done at room temperature. In practice, look at the regulated output curve if the maker publishes one, and assume shorter runtimes in serious cold.

The features that make a real difference in Nordic conditions are mundane: a switch large enough to operate in mittens, a lock-out mode so the lamp does not switch on in the pack, a red light mode that preserves night vision and is polite in shared cabins, and a battery pack that can be worn under a jacket on a cable for very low temperatures.

Power bank capacity is printed in mAh, but watt-hours (Wh) give a fairer comparison across devices, and Wh is what airlines care about: most carriers allow banks up to 100 Wh in cabin baggage without approval, while checked luggage is not permitted. Expect real usable capacity to be noticeably lower than the label after conversion losses — and lower still in the cold.

Ports are a weak point. Snow melts into USB-C sockets and refreezes; condensation forms when cold gear meets a warm cabin. Rubber port covers help, as does keeping devices in a sealed bag while they warm up indoors so condensation forms on the bag rather than inside the device. Cables stiffen and crack in the cold; braided or silicone-jacketed cables tolerate flexing better.

Solar panels deserve a sober look. Above the Arctic Circle in winter, sun angles are low or the sun is absent entirely. Panels are excellent on long spring days in Lapland, but in December they are mostly ballast.