UPDATED: Amazon has acknowledged the problem. Read its statement at the end of this article. We should see a fix soon.
I use one of my iPads and the iPhone heavily each day, often for hours at a time. I carry my iPhone 6 Plus everywhere for long days, usually 5 a.m. to 10 or 11 p.m. As my primary work system, the iPad Air 2 (or sometimes the iPad Air) is easily used for 8 - 10 hours daily.
With such heavy use I have been impressed with the long battery life of each device. The iPhone 6 Plus can last over 1.5 days regularly, and I can't remember the last time either iPad had less than 50 percent of the battery left after a very long day. That changed recently, and it appears Amazon's Kindle app is to blame.
About two weeks ago I noticed that my iOS devices were using more battery than ever before. A couple of days the iPhone was very low at the end of the day, and the same with the iPad Air 2. Each time it happened I couldn't think of anything I'd done differently. The iPhone 6 Plus and iPad Air 2 were hitting the battery harder than before.
Looking at battery usage by app in Settings>General>Usage>Battery Usage I quickly homed in on the culprit. The Kindle app from Amazon is now always the app that is using a greater percentage of my battery, and often by a wide margin.
I read a lot of Kindle books but rarely for hours at a time; a typical reading session is only 15 minutes or so. Rarely does my accumulated daily reading time exceed an hour. The usage of other apps far exceeds this, especially Safari and Evernote. These don't come close to how hard the Kindle app hits the battery.
Lately I started regularly playing Halo: Spartan Strike on the iPad Air 2, sometimes for over an hour at a time. Games can go through a battery charge pretty fast, but every time I check it after playing, the Kindle app is always showing a greater use of the battery, sometimes significantly so, than the game.
The screen image above of the battery usage on the iPhone 6 Plus was taken around mid-day. Use of the Kindle app was not heavy, in fact it was only a few minutes. It seems the app hits the battery hard even when not actively reading a book.
Since I noticed this around a couple of weeks ago I checked the version history of the Kindle app to see if it had been updated around that time. Sure enough, a minor update (version 4.8.1) was pushed to the iPads and the iPhone on April 15 (see image above). It indicates it only addresses "performance and stability improvements". Perhaps performance was enhanced at the expense of battery.
When it comes to sudden battery issues, I don't believe in coincidences, so I'll bet this update is the culprit. Searching online has not turned up any indication that this is widespread. Since I am seeing it on three different iOS devices, I doubt my situation is unique. If you've noticed a similar shortening of the battery life on your iPhone or iPad, check how much the Kindle app is using the juice. Hopefully Amazon will get another update soon to address this issue.
Amazon support forums aren't showing any complaints about this issue yet, but it's been a common complaint about other updates for two years. Amazon has not yet responded to our request for comment.
UPDATE: Amazon has acknowledged this issue and has responded to me with this statement:
..checked and see that number of eligible customers have contacted us regarding this issue and our technical team is currently working to address this problem. Once we've been alerted to such situations, of course we take steps to correct them immediately; and errors like this are usually corrected shortly after they have been reported. In this case, I request you to please wait for next 24-48 hours and I am sure this issue will surely rectify by that time.