The other day I picked up my iPhone 4S and when I pressed the home button the screen remained black. Pressing the sleep button didn’t do anything either. At first I thought the phone might be dead, but then I realized it had probably just turned itself off because the battery had run out. Indeed, it had. When I plugged it into a power source the screen came on displaying the empty battery image.
The weird thing about this was that I was pretty sure I had fully charged the iPhone the day before. I usually get about 2-3 days of light use out of my iPhone before I have to recharge it. I have all the radios (WiFi, Bluetooth, 3G) and Location Services turned on, so 2-3 days is pretty good I think. Since I wasn’t absolutely sure I had charged the phone, I just dismissed the whole issue. Then, the next day, the phone was dead again when I picked it up to use it.
This time I was positively sure I had fully charged the phone the day before. Alas, when I plugged it into a power source, it was obvious that the battery was empty and the phone had shut itself off again. This was strange. After getting 2-3 days of use/standby now I was all of the sudden getting less than a day?
I proceeded to fully charge the phone again and then closely watched the battery indicator after unplugging it. An hour later the battery had gone down from 100% to 93%. Yet another hour later the battery was at around 84% and so it continued. Something was eating power like crazy. At that rate the battery would have run out within 12-14 hours.
The phone’s usage stats were also very strange. They showed a usage time of about 50% of the overall time since the last full charge, but the phone had been entirely on standby except for the occasional battery check. Usage time should have been a couple of minutes at most, not hours.
I googled the issue and immediately found this monster thread at Apple Discussions. People were (and still are) reporting massive battery drain on their iPhones and no single solution seemed to have emerged that fixed the issue for everyone.
Many people in that thread seemed to be having battery issues since getting their iPhone, some were attributing it to faulty or incompatible SIM cards. Others suspected corrupted contacts, iCloud, 3G data usage, the Location Services Setting Time Zone setting and several other things to be the culprit, but there seemed to be no clear pattern or solid evidence. What was peculiar about my case was that the battery drain started all of the sudden, out of the blue. Had I changed anything in the last couple of days that might be causing this?
Indeed, I had. When I synced my iPhone the last time I had enabled WiFi syncing in iTunes, a feature introduced with iTunes 10 and iOS 5. I did it without thinking too much about it, it was more like: “Hey, that’s handy. I’ll activate that.”
WiFi sync automatically syncs your iPhone with iTunes only when it’s plugged into a power source. At least that’s the way it’s supposed to work. When the phone isn’t plugged in you can also initiate a sync manually. The status bar of the iPhone shows a Sync icon when it’s syncing, but this wasn’t showing on my iPhone. So even though it wasn’t actually syncing, it was definitely doing something in the background that was causing the massive battery drain.
To be sure WiFI sync was the culprit, I disabled it again, charged the phone to 100% and then kept an eye on the battery indicator over the next couple of hours. Sure enough, things were back to normal. After about 16 hours of mostly standby the battery was still at 95% and usage stats were normal (16 minutes of use and 16 hours of standby).
While I’m glad I found the cause for the battery drain, I’m not quite sure what to think of the whole issue. I’m hoping there’s a bug in WiFi syncing that causes the phone to use so much power, but there’s also the possibility that this is normal behaviour because the iPhone needs to constantly poll iTunes to check for updates it should sync and all that WiFi activity is massively affecting battery life. If the latter were the case, that would make WiFi sync all but useless, at least for me. Less than a day of standby time from a phone that’s more or less idle is unacceptable. So I’m hoping iOS 5.1 will improve things in this regard. Once it’s out I’ll be reactivating WiFi sync and keeping a close eye on the battery indicator.
