Tvoj telefón nie je mŕtvy. Je len studený.

Stane sa to skoro každému aspoň raz za zimu. Si vonku v zime, vytiahneš telefón, aby si sa pozrel na mapu, a obrazovka zhasne, hoci ešte pred chvíľou ukazovala štyridsať percent batérie. Klamala ťa vlastne batéria? V istom zmysle áno.

It happens to almost everyone at some point each winter. You are out in the cold, you pull out your phone to check a map, and the screen goes dark, even though it showed forty percent battery only moments earlier. Had the battery been lying to you? In a sense, yes.

Vnútri každého telefónu je lítiová batéria, ktorá nie je ani tak zásobníkom uloženej elektriny, ako skôr malou, neustále prebiehajúcou chemickou reakciou. Energia vzniká pri presune častíc medzi dvoma stranami batérie a rovnako ako pri väčšine chemických procesov sa tento presun pri poklese teploty výrazne spomalí. V mrazivom vzduchu sa častice pohybujú tak pomaly, že batéria nedokáže dodávať energiu dostatočne rýchlo, jej napätie prudko klesne a telefón tento pokles vyhodnotí ako vybitú batériu a sám sa vypne, aby ochránil svoje obvody.

Inside every phone sits a lithium battery, which is less a tank of stored electricity than a small, ongoing chemical reaction. Power is generated as particles migrate between the two sides of the battery, and like most chemical processes, that migration slows down considerably once the temperature drops. In freezing air, the particles move so sluggishly that the battery cannot deliver power quickly enough, its voltage collapses, and the phone, reading that drop as an empty battery, switches itself off to protect its circuits.

Dôkaz príde vo chvíli, keď sa vrátiš dnu. Chémia sa zohreje, zrýchli sa a ten istý telefón sa opäť zapne, tentoraz s možno tridsiatimi percentami, akoby sa vôbec nič nestalo. Energia tam bola po celý čas, len bola uväznená za pomalou reakciou. Preto sa v zime oplatí nosiť telefón vo vnútornom vrecku, blízko vlastného telesného tepla: batéria v skutočnosti nie je slabá, len ju tvoje počasie príliš nenadchýna. Chýbalo teplo, nie nabitie, a bolo tomu tak celý čas.

The proof arrives the moment you step back indoors. The chemistry warms up, speeds up, and the very same phone switches back on showing perhaps thirty percent, as though nothing had happened at all. The energy had been there the whole time, merely trapped behind a sluggish reaction. Which is why, in winter, it pays to keep your phone in an inner pocket, close to your own body heat: the battery is not actually weak, it is simply unenthusiastic about your weather. Warmth, not charge, was the missing ingredient all along.