I have an iPhone 5S. Since I do technical support for a living, I don't need the latest phone. Every two years if just fine for me. After two years, my phone is a little beat up and starting to under-perform, and I am excited to get the latest model.
When iOS 8 came out, I read about issues with poor battery life, but I didn't experience them at first. It was probably three or four months ago when my battery life became just terrible, and I could no longer get through a day. That was about the time when iOS 8.2 came out. Now I am on 8.3 and it is as bad or worse.
I started digging into the problem and found that iOS 8 comes with a setting called Battery Usage (Settings > General > Usage > Battery Usage). When you tap on it, wait for a few seconds. At first I thought nothing was happening. Then a lot of information comes in, including battery life suggestions and the percentage of usage during both the last 24 hours and the last seven days.
The first time I checked my usage, the culprit was (unsurprisingly) Maps. I wasn't surprised, but I did think I was taking steps to avoid the problem. Since I knew Maps sucked the life out of my battery, I always used it while plugged into a car charger. And I always hit END when I arrived at my destination. It turns out that is not enough.
Now what I do is "force quit" the Maps app after after I hit END. To do that, I double-tap on the home button. I can then see previews of recently used apps (in the order I used them). I could swipe to the left to scroll through them, but don't need to. I see that Maps is the second app from the left and swipe it up to force it to quit.
Now Maps doesn't show at all in my battery usage because my phone is charging when I use the app, and Maps is turned off when I am not using it.
Problem solved? Not quite.
The screenshot above shows my current usage. You can see that I have made it to 10:38pm and have 24% of a charge. It used to last the entire day with a 70% charge, so what's the problem? Low Signal is the problem.
Since I can't keep the iPhone from constantly checking for a connection when the signal is poor, I can work around the issue in two ways. The first area of concern is Mail.
In the Mail settings (Settings > Mail, Contacts, Calendars > Fetch New Data), I see that PUSH is turned on. There are two alternatives to PUSH: FETCH and MANUAL. (Actually, PUSH is not always an option, but FETCH and MANUAL are.) Unfortunately, there are two points of view on whether PUSH saves battery life vs FETCH (some say it does and others that it makes it worse).
I am pretty sure that iOS 8 turned on PUSH. Before that, I had it set to MANUAL. So I am going back to the MANUAL setting. That means my iPhone will only receive email when I am actively using the Mail app. At least I hope that is what it means. It could be that I have to force quit the Mail app to stop it from checking for email all day. Anyway, the result will be that my contacts and calendars won't sync until I have those apps open (or active), so there will be some delay in getting everything to be up-to-date when I want to schedule something or use contacts.
The second problem area is Personal Hotspot. The way it is supposed to work in iOS 8 is that my laptop or iPad checks to see if my iPhone is nearby, and turns on the hotspot when I choose it from my Wifi network list. When I stop using the device (laptop or iPad) it is supposed to turn off the hotspot. It often doesn't. So I will have to go back to changing those settings manually to lower my battery usage.