Late last week, Mrs. Sande (my wife, not my mom) pointed out to me that her iPhone 5s screen was popping out. What she meant by popping out was that the screen was being pushed out in areas by something and was literally bulging above the top of the display. Knowing her charging habits for that iPhone, I immediately knew what was happening. This image from mommytasking shows a really bad case of the bulges:
The lithium ion (Li-ion) batteries that power a lot of our mobile electronics these days have a problem with being plugged in all the time. I've seen it with older MacBooks with removable battery packs -- usually someone would complain of not being able to use the trackpad or that certain keys on the keyboard suddenly weren't working properly, and sure enough, if I pulled the battery pack I noticed that it was swelling.
The issue arises when a device -- like a laptop that's used as a primary Mac or an iPhone that's constantly getting a charge from a battery case -- is plugged most of the time. After about two or three years of this, the battery packs often begin to swell. Sure enough, Barb's iPhone was almost always being charged. First, it was sitting in a Mophie battery case that was set up to always discharge first, so as far as the iPhone was concerned, it was plugged in and being charged. Next, when she was at work, she'd plug in the Mophie case to keep it topped off. Except for those times when she was using the iPhone away from work and the Mophie case was discharged, that phone always thought it was plugged in.
We'll be going to the store next week to get her a replacement iPhone -- most likely an iPhone 6s Plus -- but I'm going to insist on two things. 1 - that she not use a Mophie case on the device and 2 - that she avoid plugging the iPhone in for charging until it's below 20% of full charge. "Exercising" the battery by allowing it to go through a full or even partial charge/discharge cycle every day is much better for the battery than keeping it charging all the time with an external battery case or pack, or keeping it plugged in.
Can one of these bloating (that's the industry term) batteries cause problems other than pushing the display out? Yep. In some rare cases, they'll short internally and either explode or otherwise combust. That's not something that you want to have happen while the phone is in your pocket or purse.
The moral of the story? Let your iPhone (or iPad) battery work out. Let it charge up, then let it discharge as far as you can before recharging again.