Lithium-ion batteries, like those in iPhones, have a longer useful life if you do not charge over 80%. But to keep the day you probably want a full charge. With iOS 13, Apple can bring you the best of both worlds.
iOS 13 will charge 80% and wait
Apple announced iOS 13 at WWDC 2019. Buried in the list of extras was a note on "battery optimization." Apple says it will "reduce the time your iPhone spends Full charge. "Apple will specifically prevent your iPhone from charging over 80% until you need it.
You may be wondering why Apple wants to keep your iPhone at 80% charge. It's about how lithium-ion battery technology works.
Lithium-ion batteries are complicated
Batteries are generally complicated technology, the basic goal is to squeeze as much energy as possible into a small space as possible and then release that energy without causing a fire or explosion. It's a juggling of priorities.
Lithium-ion batteries make things extra complicated Previously rechargeable technology suffered from memory effect – essentially, batteries lost their maximum capacity if you constantly recharged them after only partially discharging them. Lithium-ion batteries do not have that problem. If you still drop the battery to drain before recharging, you should stop. You damage the health of the battery.
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You should not keep your battery at 100%
Lithium ion batteries charge 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 in the past. Nor does it have the dreaded "memory effect" that causes the battery to lose its full capacity.
Instead of having a memory problem, Li-ion has a maximum problem with the charge cycle. You can only charge the battery so many times and then it starts to lose capacity. It is not just charging zero to 100% that counts as a full charge. If you charge from 80 to 100% five days in a row, these 20% fees add to a "full charge cycle."
Not only emptying the battery to zero and then charging to 100% damages your battery in the long term, always charging the battery is not good for that either. By staying close to 100% you risk overheating the battery (which can cause damage). In addition, to prevent your battery from "overcharging", it also stops charging for a while and then restarts.
This means that if you charge your device overnight after it hits 100%, it drops to 98 or 95% and then charges back up to 100% and repeats the cycle. You use your maximum charging cycles without even using the phone actively.
The solution: the 40-80 rule
For all these reasons and more, most battery manufacturers will recommend the "40-80 rule" for lithium-ion. The rule is straightforward: try not to drop your phone too much (less than 40%), which can damage the battery, and try not to keep your phone fully charged (more than 80%) all the time.
Either scenario is exacerbated by the weather, so if you want your battery to maintain its full capacity longer, keep it around 80%.
iOS 13 Sits at 80% During the Night
New iOS updates include a battery health feature that lets you check your battery capacity and see a history of your battery usage. The feature is a useful way to know if you have adhered to the 40-80 rule.
But Apple knows you don't want to start the day around 80%. If you travel a lot or otherwise are often out of reach of an outlet, the extra 20% can easily be the difference in whether your iPhone makes it to the end of the day. Staying at 80% risks losing a valuable asset, your phone. That is why the company wants to meet you in the middle.
In iOS 13, a new charging algorithm will keep your iPhone at 80% when charging overnight. That algorithm will determine when you usually wake up and start the day and restart the charging sequence to give you a fully charged battery when you wake up.
That means your iPhone won't spend all night not charging it. t need (and risk overheating), but when you start the day you should have 100% battery charge. It is the best of both worlds to give you as long battery life as possible, both to maintain the battery's full capacity and to make it through the day.
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