I noticed this morning that my iPhone 12 Pro Max (running iOS 16.3.1—yes, I know I’m way behind on OS updates, I have my reasons) was draining battery a lot faster than usual. I was down to less than 60% power shortly before noon, after having been charged to 100% at 7:30 am; normally, I’m around 80% at that time. I hadn’t been doing anything with it that I don’t normally do in the morning. I do not normally need to charge it during the day (I charge it overnight), and the battery health is good (98% capacity, optimized charging turned on).
I didn’t really have time to investigate it when I noticed it; I simply plugged it in to charge for a while. After that top-up charge (to about 80%), it seemed to be using normal amounts of power again for the rest of the day.
Later, in the evening, I had a moment to look into what was happening. The Battery usage info showed that in the past 24 hours, 51% of battery usage was by Mail, with 1 hour 6 minutes of activity, all background. The graph shows a pretty sudden, steep decline between 9:00 and 10:00 am, leveling off to more normal drain after that. In the past ten days, Mail’s power usage was 7%, with 2 hours 12 minutes, all background.
This baffles me. I use Mail on my phone very infrequently, only when I need to check something in my mail when I’m out and about. I checked open apps to see if I’d inadvertently left it doing something, and found it several apps back in line, displaying a PDF I had opened from an email sometime last week. I haven’t actually used Mail on my phone since the day I opened that PDF. I have sent a few emails from my phone through other apps via Sharing since then, but not in the past couple of days, nor have I made any changes to any of my accounts. I do not allow iOS Mail to check email in the background.
The only thing that seems to correlate with the time that shows the excessive drain was that I had had difficulty sending an iMessage to my spouse shortly before 9:00 am this morning, in the middle of a conversation, and I had to turn iMessage off and on again to get it to work. That lasted less than two minutes.
What could Mail have been doing, in the background, unprompted, that would cause it to use so much power in so little time? Does activating iMessage create background activity in Mail, and is it reasonable for that to last an hour?