How iOS 13 Will Save Your iPhone’s Battery (by Not Fully Charging It)

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Lithium-ion batteries, like those in iPhones, have a longer usable life if you don’t charge above 80%. But, to last the day, you probably want a full charge. With iOS 13, Apple may give you the best of both worlds.

iOS 13 Will Charge to 80% and Wait

Apple announced iOS 13 at WWDC 2019. Buried in the list of extra features was a note about “battery optimization.” Apple says it will be “reducing the time your iPhone spends fully charged.” Specifically, Apple will prevent your iPhone from charging above 80% until you need it.

You might be wondering why Apple wants to keep your iPhone at 80% charge. It’s all about the way Lithium-ion battery technology works.

Lithium-ion Batteries Are Complicated

Battery image showing the first 80% is fast charge, final 20% is a trickle charge — Apple

Batteries, in general, are complicated technology. The fundamental goal is to cram as much energy as possible into a small a space as possible, then safely release that energy without causing a fire or explosion. It’s a juggling act of priorities.

Lithium-ion batteries make things extra complicated by being rechargeable. Earlier rechargeable technology suffered from the memory effect—essentially, batteries lost track of their maximum capacities if you constantly recharged them after only partially discharging them. Lithium-ion batteries don’t have that problem. If you’re still draining your battery to empty before recharging it, you should stop. You’re damaging your battery’s health.

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You Shouldn’t Keep Your Battery at 100%

Charge showing depletion cycle, depleting 75% now, and 25% later equals 1 cycle even if you charge between. — One cycle consists of depleting an amount that adds to 100%. Apple

Lithium-ion batteries charge to 80% faster than previous battery technologies did. For most people, 80% is enough to make it through the rest of the day, so it gives you what you need sooner. It also doesn’t have the dreaded “memory effect” that causes the battery to lose track of its full capacity.

However, instead of having 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% that counts as a full charge. If you charge from 80 to 100% five days in a row, those 20% charges add up to one “full charge cycle.”

Not only does draining the battery to zero and then charging to 100% 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 damage). Additionally, to prevent your battery from “overcharging,” it stops the charge for a while, then starts again.