July 18, 2025, 1:02 pm | Read time: 3 minutes
TECHBOOK editor Adrian Mühlroth has been wondering for a while why the battery in his iPhone 15 Pro Max lasts much shorter than others. Now it’s clear which feature is to blame. The use of two SIM cards significantly drains the iPhone battery.
Many iPhone users are unaware that one of the biggest battery consumers is the connection to mobile networks. Especially when the smartphone has poor reception, the modem requires a lot of power to connect to a network.
Dual-SIM Drains iPhone Battery Twice as Fast
For smartphones with dual-SIM support, this can significantly limit battery life. The modem must now stay connected to two networks simultaneously. iPhone users report on Reddit that their battery life is practically halved by using two SIM cards. Although the iPhone Xs already allowed the use of two numbers through the integration of eSIM, especially in newer models, a significantly increased power consumption due to the dual-SIM function is noticeable.
Newer iPhones like the 15 Pro may have an additional antenna that allows parallel use. In earlier models like the iPhone 13 Pro, one SIM card interrupts the connection when a call is made with the other. I can confirm that this is no longer the case with my personal iPhone 15 Pro Max.
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What iPhone Users Can Do to Save Battery
Unfortunately, there is no perfect solution for dual-SIM users. Those who truly need two active phone numbers must accept the associated power consumption. Often, a private and a business number are used in the dual-SIM scenario–and here lies potential for saving battery.
Also read: 5 Tricks for More iPhone Battery Life
1. Turn Off Business Number Outside of Work Hours
Of course, during work hours, one should remain as reachable as possible. After work, however, turning off the SIM card is important. This can be done manually by selecting the work SIM in the settings under Cellular>SIMs and then turning it off by tapping the slider at Enable This Line.
This requires users to remember to turn the SIM off and back on every day. However, there is also an automated solution that can be set up via the Shortcuts app. It’s a bit more complicated but works automatically once set up.
- Open the Shortcuts app and tap the plus symbol in the Shortcuts tab.
- Search for “If” in the search bar and click the result.
- Press “Condition” in the new field and select “Current Date.”
- Click “Current Date” and choose “Time.” Then select the end of work time in the new “Time” field.
- Then press “is” and subsequently “is after.”
- Search for “Toggle Cellular Plan” in the search bar and select the result.
- Hold the new field and drag it directly under the “If” field.
- Press “Cellular Plan,” select the work SIM, and then set the option to “Off.”
- Repeat the process from step two with the start of work time and select the “On” option.
In the end, the shortcut should look something like this:
2. Use a Second Device for Business Number
While it’s convenient to combine personal and business numbers in one device, separating the two is recommended not only for work-life balance but also to preserve the battery in your smartphone. Employers often provide a separate mobile device. Alternatively, using an older device that might still be lying around at home is a solution.