Why Your iPhone Turns Off Automatically in Stifling Weather

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In cold weather, like winter, iPhones frequently experience sudden system shutdowns. Why do phones struggle to withstand cold temperatures and force shutdowns, even with over 50% battery life? Let's find out why today.

iPhones feature a power management chip called the Power Management Unit (PMU) embedded on the motherboard. The PMU is responsible for sharing the necessary voltage to nearly all power-hungry components, including the CPU, memory, and battery, and is one of the most powerful pieces of hardware within the iPhone.

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The PMU not only supplies power but also performs a forced shutdown function, which typically occurs at temperatures ranging from -1°C to 0°C to 10°C. iPhones lack a dedicated internal heat-dissipation system. Therefore, high-conductivity metals, such as aluminum or titanium, are often used to quickly dissipate heat generated within the device. While high thermal conductivity can effectively dissipate heat generated within the device, it can also have the opposite effect.

In low temperatures, such as winter, external cold air can easily enter the iPhone's interior. This can cause freezing within the iPhone's components, dramatically slowing down the movement of lithium ions. This slowing of ion velocity means a drop in voltage, which can indicate problems with transistors, the smallest electronic switches.

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If a voltage drop causes a transistor malfunction (a momentary interruption in the electrical circuit flow), this can lead to data corruption.

This is why the PMU's hardware-level forced shutdown feature remains in place today to prevent this situation. When performing high-load tasks (e.g., phone calls, high-end games, video recording) in low temperatures, the software may not be able to supply sufficient voltage, leading to data corruption. The PMU prevents this and, as a solution, initiates a forced shutdown (system shutdown).

The best solution to frequent forced shutdowns lies in battery performance. Check the maximum performance level under Settings -> Battery -> Battery Health and Charging. Typically, if the battery's maximum performance level is above 80%, the baseline output voltage margin is high, making PMU shutdowns rare even in low temperatures.​

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One of the characteristics of lithium-ion batteries is that the higher the remaining battery capacity, the higher the base output voltage. This means that if your current battery capacity is over 50% and your maximum performance is over 80%, you should be able to avoid sudden shutdowns even in winter. If your battery capacity is below 80%, it might be worth considering a hardware replacement at an Apple Authorized Service Center or a trusted repair shop.

I've seen people with batteries that had plenty of charge remaining but only had a maximum battery capacity of 73%. They experienced shutdowns due to high-load tasks like phone calls, even in temperatures between 10 and 15 degrees Celsius. This situation demonstrates that "maximum performance is a priority over battery capacity." Knowing this, I recommended a hardware replacement at a repair shop.