Why does the iPhone suddenly turn off?

Your iPhone goes out, although the battery still has some charge? Especially on cold winter days, this is not a rare phenomenon. atechbook explains what’s behind it and what you can do about it.

Does your iPhone battery sometimes do what it wants? Even though the display still shows 20 percent charge and you’re sure you’ll make it home, the smartphone just turns off. And when it’s plugged in, it suddenly jumps from 0 to 10 percent and more. But what is the reason for this?

Also interesting: How to find out if someone is hijacking your WLAN

Why does the iPhone simply turn off?

The answer is quite simple: Because the battery does not deliver. Over time, a battery loses power. If the power is not enough to meet the demand, iOS pulls the plug. This prevents the system from further damaging the battery.

This happens especially with older iPhones that have already gone through several charging and discharging cycles. Charging to 100 percent and discharging to 0 percent is particularly hard on the iPhone. To ensure that the battery lasts for a long time, it is recommended to keep the charge between 20 and 80 percent. At night, the iPhone does this on its own. Here it charges to a maximum of 80 percent and only charges to the full 100 percent in the morning shortly before getting up.

Especially cold winter days put additional strain on the battery chemistry. Here, it can happen even faster that the iPhone jumps from “the battery will last until home” to “completely dead”.

Also interesting: That’s why the battery on the iPhone is sometimes yellow.

iPhone just turns off – what can you do?

After it came out that Apple was intentionally throttling the speed of older iPhones to preserve battery performance, there were many negative headlines. As a result, the company has become much more transparent with its batteries. In the battery overview in the iOS settings, you can now see the details of the battery state.

Check the battery power in the settings

It can be quickly checked how much capacity the battery still has and whether it still supports maximum performance. The capacity indicates how much charge the battery can still hold compared to the delivery state. It’s not uncommon to lose between 5-10 percent of battery power in just two years. Depending on how often you charge the battery and expose it to adverse conditions like heat and cold, the capacity can be severely limited.

Related: Checking battery capacity and performance on the iPhone

More interesting for the question why the iPhone just turns off, however, is the peak performance. When the battery power decreases over time, the voltage that the battery can supply also decreases. If the voltage demanded by apps exceeds that of the battery, the iPhone simply shuts down.

Apple explains this process in great detail on its support page. However, the essence of the shutdown is that iOS automatically turns on the power management. Thus, the system prevents apps from demanding more performance than the battery can deliver. In plain language, this means that the overall performance is reduced.

In the worst case, the only thing that helps is battery replacement

If the iPhone battery no longer delivers maximum performance, the system can be set to reduce the power in the settings. However, it can then happen again and again that the iPhone goes out prematurely. The only alternative is to replace the battery. This costs 73.11 Euros for the iPhone X or newer and 53.61 Euros for the iPhone SE 2020 and iPhone 8 and older at Apple and certified repair partners.


  • Apple