“It Won’t Charge Past 80 Percent” — No, Your Phone Isn’t Broken, It’s Trying to Protect Its Battery

If you've ever owned a piece of consumer technology, then there's a good chance you've experienced battery degradation at some point or another. Due to the way lithium-ion power packs are constructed, fully depleting a charge and leaving it depleted can result in these cells dying, minimizing a battery's overall maximum capacity, or killing the pack for good. On the flip side, over-charging it, i.e., keeping it plugged in past 100 percent, can also contribute to long-term degradation as well.

And as it turns out, it's this phenomenon that can answer a question so many iOS users have. Which is: Why does my phone stop charging at 80 percent?"

On June 5th, 2019, Apple announced its plans to implement Optimized Battery Charging as a feature on iOS devices sporting lithium-ion power packs as part of its iOS 13 update. Subsequent updates featured revisions to this functionality, which serves to extend the lives of user's batteries on their iPhones and iPads.

The software is designed to learn an individual user's charging habits and adapt to them as a means of reducing the number of power cycles a phone goes through. Additionally, it prevents the phone from persistently remaining at 100 percent capacity.

According to Midtronics, there are a slew of adverse effects that can come as a result of overcharging a battery.

To understand why this is the case, a basic understanding of how lithium-ion batteries work helps. This guide from UL Research Institutes provides a very thorough breakdown, but basically, these lithium-ion cells move within individual battery packs, which have a preset capacity.

Since these cells are moving between the anode and cathode inside the battery, there is a slew of barely imperceptible motions occurring constantly within the battery. And technically, a fully charged battery is heavier than one that isn't charged, even if the most sensitive of measuring tools are incapable of clocking this weight disparity.

And while many batteries and consumer technologies are outfitted with failsafes to ensure that batteries aren't over-charged, that doesn't mean keeping them plugged in at 100 percent is a good idea. That's because in order for these lithium-ion cells to operate smoothly, they need room to do so.

Keeping the cells fully charged doesn't give them that "space" to move, consequently inhibiting some of this anode cathode movement. This doesn't mean you should go around shaking your batteries, but rather, this speaks to the process of the lithium ions moving between these electrodes.

So overcharging, as Midtronics writes, can lead to overpowering a battery, which can, in turn, result in it overheating and swelling. Once those battery packs expand and burst, you're going to have a nasty mess of chemicals to deal with. And maybe even a fire.

Inhibiting this movement between electrodes can cause some parts of the battery's cell to die out. Hence why your batteries may not hold a charge as well as they used to. In order to curb that from happening, Apple and other tech companies have introduced adaptive charging protocols.

For instance, Tesla even recommends keeping one's car charged only to around 80 percent in order to preserve the life of its massive lithium-ion battery packs. Topping off to 100 percent should be reserved for long-distance driving and road trips.

Google's Android OS also has an adaptive charging feature as well, "trickle charging" one's smartphone after hours, presumably when folks are about to go to sleep and plug their phone in for the night.

If you have an Android phone and want to customize adaptive charging, or disable it completely, head on over to the phone's Settings app > Battery > Battery Health > Charging Optimization.

On an iPhone, head to Settings > Battery > Battery Health & Charging. Then, you can turn Optimized Battery Charging on or off.