Why does cold kill battery?

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I live in the polar vortex and so walking outside I’ve had a full phone battery go dead in under twenty minutes. We’re talking idk ≈ -40F. When it’s warmed up again there it is suddenly at 60%. I don’t expect to understand well because I know little about batteries, but what’s the deal? And how is it that once it’s warmed it is not only fully functional but has retained charge? At what temperature does this effect begin to take hold?

In: Technology

The energy stored in batteries is released via a very carefully controlled chemical reaction, and like all chemical reactions they can be positively or negatively affected by temperature.

For many batteries, at lower temperatures it takes more of the battery’s potential energy to keep the reaction going vs. actually power the electronics in your phone.

>At what temperature does this effect begin to take hold?

That depends entirely on the specific chemistry of your phone’s battery, and that’s not something that would be precisely known (it’s presumably a lithium-based battery, but we don’t know what specific variety of lithium battery it is).

Along with sulfuric acid, water is inside of batteries and helps to transport electrons from the negative side of the battery to the positive terminal. When the water is frozen it still conducts electricity. Just horribly. Therefore your battery will act as tho it is drained. Get the battery back above freezing temperature should help restore the issues.

Batteries provide electrical power by means of a chemical reaction. This chemical reaction slows down in colder temperatures, causing it to not be able to put out as much current, and even causing its voltage to drop. The energy is still there, but the battery just can’t put it out there as fast as it normally would. A device like a phone typically doesn’t measure the actual amount of energy remaining in its battery… rather, it measures its voltage and calculates its energy from that. This is why when you take the battery indoors or otherwise warm it up, the energy seems to “come back”.

The battery is not empty, but the capacity cannot be fully utilized because the cold increases the resistance of the cells which decreases the current up to a point where the phone can no longer be used.

The capacity you see is calculated by means of software or dedicated chips and these contain algorithms to decrease the displayed capacity value at lower temperatures to be aligned with this behavior. When the temperature rises this so called state of charge gets calculated higher again.

The temperature limits depend on the cell chemistry. But for LiPo cells, this effect can already be noticed above the freezing point and things start getting really bad below -20 °C. Charging is worse, charging a battery below freezing point is often considered to be damaging.