Wi-Fi Calling kills iPhone battery life – how to fix it

23 July 2016, 04:22

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I switched to an iPhone SE a few days ago and, while I’m happy with the diminutive device, I’ve been a little worried to see battery life draining incredibly quickly. I would take the device off charge and after an hour of non-use the battery would be down to 90%. A full working day’s standby brought it down to 10%. This was very odd because all the reviews said that iPhone SE had superb battery life, and perhaps even better than the iPhone 6S.

I removed various apps that Settings > Battery reported were eating juice. Gone were the news apps I had installed that fed me news flash notifications. However, battery life was STILL gobbled-up. I eventually realized the bad guy in the picture was the Wi-Fi Calling feature. Back into the Settings app I went, and tapped Phone > Wi-Fi Calling, and disabled it.

It was a miraculous fix. The battery percentage figure now barely changes across an hour of non-use.

A possible workaround
A workaround I haven’t tried for those who still want to use Wi-Fi Calling is to turn off the cellular radio entirely. The reduction in power for the cellular radio will balance out the extra juice required for the Wi-Fi Calling feature. The downside is obvious. If you leave your home or office, and forget to enable cellular, then your phone is entirely without a signal.

Start by ensuring Wi-Fi Calling is turned ON.

Following this, turning off cellular and relying only on Wi-Fi Calling is easy but the required steps probably aren’t what you might expect. Open the Control Center by sliding up from the bottom of the screen, and enable Airplane Mode. Then tap the Wi-Fi button to enable it. Cellular and Bluetooth will remain turned off, but because Wi-Fi is now enabled, Wi-Fi Calling will work just fine. (Note that you can also enable Bluetooth when Airplane Mode is switched on.)

An explanation
So, what’s happening to make Wi-Fi Calling chew-up battery life? Working-out what technology underpins Wi-Fi Calling is annoyingly difficult. Nobody seems to know for sure but I’ve read a few times that Wi-Fi Calling creates a secure Internet tunnel to the cellular provider in order to route calls. This tunnel is active all the time, which is why the battery life is drained. It’s a little like constantly using the web browser, although that’s not quite a perfect analogy because I suspect much less data is transmitted regularly within the secure tunnel. But you get the idea.

If you’re reading this and thinking, damn, I bought my phone for the Wi-Fi Calling feature then you’re not alone. I did too, because cellular reception where I live is essentially non-existent. Who knows, Apple might improve the Wi-Fi Calling implementation in a future release of iOS. We also shouldn’t forget that not only is the technology relatively young but it’s also supported only by a fraction of the world’s cellular providers. This is why, right now, nobody’s making a fuss about how the feature eats battery life. I reckon Wi-Fi Calling will be mainstream in about two year’s time, and articles like the one you’re reading now will be pretty much everywhere.

Personally, I’m now going to enable Wi-Fi Calling only if I need a signal in an area where there are no bars of reception (as happens a lot when visiting out of town places like cafes that have free Wi-Fi). I’d like to see the ability to enable/disable Wi-Fi Calling added to the Control Center so that it’s easy to both switch on and off, and to see when it’s active.

UPDATE: It seems from the comments below that some people are skeptical that Wi-Fi Calling is having a negative effect on battery life. If in doubt, just Google to see many other stories of this happening. Also, see the following Apple Support forum discussion, from which I quote:

I wanted to find some way to quantify the effects of Wi-Fi calling on my phone, so I did some searching in the App Store and found an app (System Status – activity monitor, network info, battery charge & memory manager) that allows me to monitor CPU, Battery, Memory usage of my 6s. It shows that as soon as WiFi calling is triggered (turned on & activated by a poor cellular signal), my CPU usage jumps from the 5-10% range to a minimum of 50% and stays there as long as WiFi calling is active. I have confirmed that it is not the fact that WiFi Calling is switched on, but it must be active (Wi-Fi appears in the status area next to AT&T.) Moving to an area of good cellular signal drops the CPU usage as soon as the phone stops using the feature (even though it’s still enabled in the settings.)

UPDATE #2: I’ve noticed that using WiFi Calling when on a 2.4GHz network, rather than 5GHz, seems to drain the battery much less savagely. Previously I’d been using 5GHz exclusively. A quick Google reveals what I suspected, which is that 5GHz typically requires more battery power than 2.4GHz because the signal has to “work harder” to get through the likes of walls and ceilings. Additionally, Wi-Fi hardware running at 5GHz sucks marginally more power (which might explain why the Apple Watch only uses 2.4Ghz WiFi, for example). In other words, the constant need to keep alive a connection for WiFi Calling across 5Ghz WiFi might’ve been the cause of my iPhone SE’s battery drain.

Other people have been finding, as in the comments below, that a MTU setting on the router of anything other than 1500 can cause power consumption issues when using WiFi. If your router allows you to change this (mine doesn’t) then this is worth investigating.

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It’s probably a combination of wifi-calling and the terrible reception near you. I don’t think it’ll be a widespread problem, though.

It doesn’t drain my battery, but I have good cell reception nearly everywhere in my area. I suspect that your poor reception is causing a large part of the drain, and that the phone keeps switching between wifi and cellular, and the constant changes are contributing to the battery drain.

— Joel42 · Jul 23, 05:50 AM · #

Joel, the SE isn’t my first iPhone :-) And I’ve always had poor reception in my area. The battery has never drained as quickly as it does with Wi-Fi calling enabled.

Take a look at this Apple forums discussion thread, amongst others – lots of people are reporting this:


Some people have reported that, when the iPhone’s used when Wi-Fi Calling is enabled, the battery drains by 1% every MINUTE!

Keir · Jul 23, 05:54 AM · #

Hi Kier,

I’m a loyal reader, so it was a bit strange to see myself quoted from my support forum posting. Back in March/April, when I was having the problem, I posted to the Apple forums and to macintouch.com. When I found the solution to my issue, it looks like I only posted to macintouch.com.

I was able to fix the issue, since it only occurred at my office (luckily I’m the IT Director) and I use Wi-Fi calling there everyday now with no impact on my battery. Here’s what worked for me:

Follow Up 4/11/16:

Looks like I found the issue.

The only location where I have access to WiFi and the LTE signal is weak enough to trigger WiFi calling is here in the office. This weekend I used Airplane mode to force WiFi calling at my house and there was no problem with the CPU issue. I did some tests using a Verizon MiFi and WiFi calling worked without any issues. So when I got back in the office this morning, I switched to our guest network and the issues were still there. Tested from the office with the MiFi and no problems.

Began to suspect that it was an issue with our Sonicwall settings, so I did started looking at the network requirements for WiFi calling and came across a post on the Apple Support Forums that mentioned that the MTU Size needed to be 1500 and our Sonicwall’s MTU size on our primary WAN connection was set at 1404. I bumped that up to 1500 and turned on WiFi calling – no CPU problems so far.

— Brackintosh · Jul 23, 10:39 AM · #

Wow… thanks for the advice. I will note it for the future.

Anders · Jul 24, 08:10 AM · #

I think apple just simply should make a normal battery. They will see millions of iphone batteries in trash bags after Neutrino Inc selfcharhing battery will be released.

— Basil67864 · Jul 24, 09:40 AM · #