Tvoj telefon nije mrtav. Samo mu je hladno.

To se gotovo svima dogodi barem jednom svake zime. Vani si na hladnoći, izvadiš telefon da provjeriš kartu, i ekran se ugasi, iako je samo nekoliko trenutaka ranije pokazivao četrdeset posto baterije. Je li te baterija lagala? U određenom smislu, da.

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.

Unutar svakog telefona nalazi se litijska baterija, koja je manje spremnik pohranjene struje, a više mala, neprestana kemijska reakcija. Struja nastaje dok se čestice kreću između dviju strana baterije, i kao i kod većine kemijskih procesa, to se kretanje znatno usporava kada temperatura padne. Na ledenom zraku čestice se kreću toliko sporo da baterija ne može dovoljno brzo isporučiti struju, njezin napon naglo padne, a telefon taj pad tumači kao praznu bateriju i sam se gasi kako bi zaštitio svoje sklopove.

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.

Dokaz stiže u trenutku kada se vratiš u toplo. Kemijska reakcija se zagrije, ubrza, i isti se taj telefon ponovno upali, pokazujući možda trideset posto, kao da se ništa nije dogodilo. Energija je cijelo vrijeme bila ondje, samo zarobljena iza spore reakcije. Zato se zimi isplati držati telefon u unutarnjem džepu, blizu topline vlastitog tijela: baterija zapravo nije slaba, samo nije oduševljena tvojim vremenom. Toplina, a ne napunjenost, bila je taj nedostajući sastojak.

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.