Two weeks ago, Apple announced details about iOS 13 at their Worldwide Developers Conference (WWDC), and buried in the list of extra features coming with the new operating system was a brief note about “battery optimization.” In the note, Apple says it will be “reducing the time your iPhone spends fully charged.” In other words, through the new iOS, Apple will prevent your iPhone from charging above 80 percent in an effort to save your device’s battery lifecycle. And the reason why has to do with the way lithium-ion battery technology works.
Batteries, in general are complicated pieces of technology. The fundamental goal is to cram as much energy as possible into a space as small as possible, then safely releasing that energy without causing a fire or explosion. It’s a juggling act of priorities.
Before lithium-ion batteries, earlier types of rechargeable batteries suffered from something called ‘memory effect,’ which means that they lost track of their maximum capacities if they were constantly recharged after only being partially discharged. Now, today’s lithium ion batteries can charge to 80 percent much faster than its predecessors. To reach a complete 100 percent charge, users would have to wait a bit longer as it takes more effort for the lithium-ion battery to reach a full charge. And luckily, for most people 80 percent is enough to make it through the rest of the day, so it gives you what you need sooner. They also do not have the dreaded ‘memory effect’ that causes batteries to lose track of their full capacity.
However, instead of a memory issue, Li-ion has a maximum charge cycle issue. You can only recharge the battery so many times, and then it starts to lose capacity. It’s not merely charging zero to 100 percent that counts as a full charge. If you charge form 80 to 100 percent five days in a row, those 20 percent charges add up to one “full cycle charge.”
Not only does draining a battery to zero and then charging it to 100 percent hurt your battery in the long run, always charging the battery isn’t good for it either. By staying near 100%, you risk overheating the battery, which can cause terrible damage. Additionally, to prevent your battery form “overcharging,” it stops the charge for a while, then picks it back up after a while.
And for these reasons, most battery manufacturers will recommend the “40-80 rule” for lithium-ion. The rule is straight forward: try not to let your phone deplete too much (less than 40 percent), which can damage the battery, and try not to keep your phone charged entirely (more than 80 percent) all the time.
But Apple knows that most people don’t want to start the day around 80 percent. If you travel a lot or otherwise find yourself frequently out of reach from an outlet, the extra 20 percent can easily be the difference in whether your iPhone makes it to the end of the day. Staying at 80 percent risks losing a valuable asset, your phone. That’s why the company wants to meet you in the middle.
In iOS 13, a new changing algorithm will keep your iPhone at 80 percent when charging overnight. The algorithm will determine when you typically wake up and start the day, and reset the charging sequence to give you a fully charged battery when you wake up. That means your iPhone won’t spend the entire night taking a charge it doesn’t really need (and risk overheating and starting a battery fire), but when you start your day, you’ll still have a 100 percent battery charge. It’s the best of both worlds to give you as long as battery life as possible, both in retailing the full capacity of the battery and making it through the day.