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How Best to Charge Your Phone, Explained by an Expert

Welcome to Product Support, a column devoted to helping you get the most out of the gadgets and software you already use.

Keeping your gadgets charged is easy in the short term. Just keep an eye on their battery levels and plug them into the wall when they gets low. But keeping your gadgets’ batteries healthy in the long run is a much more complicated proposition. The lithium-ion batteries that are in virtually all of our gadgets are chemically destined to degrade over time, holding less charge than they used to, and blowing through what little they have faster then before. It’s impossible to stop this process, but it is possible to slow it.

To find out the best ways to postpone the inevitable, we talked to Isidor Buchmann, CEO and founder of Cadex Electronics and main contributor to extremely in-depth and invaluable online resource Battery University, about how exactly you should treat your batteries in a perfect world, what you can do to maximize their life.

So brace yourself, because here’s what you’re probably doing wrong.

Is it bad to charge my phone to 100 percent?

For optimized battery life, your phone should never go below 20 percent or never above 80 percent. It may put your mind at ease when your smartphone’s battery reads 100 percent charge, but it’s actually not ideal for the battery. “A lithium-ion battery doesn’t like to be fully charged,” Buchmann says. “And it doesn’t like to be fully charged and warm.”

Is it bad to run your phone down to zero?

Letting your phone reach zero percent (aka, die) is not great for the long-term heath of its battery. This is because each time it reduces the number of cycles left on its Lithium-ion cell. The fewer number of cycles, the less amount of charge it’s able to hold and the shorter the life of the battery.

At what percentage should I charge my phone?

In a perfect world, your battery never goes below 20 percent, and also never above 80 percent.

Electric vehicles, with batteries that are required by various regulations to have a minimum operational life on the order of several years, make that prospect more feasible than it is for your phone by using drastically oversized batteries that are purposefully designed to never be fully charged. “You’ll typically charge to about 80 percent and discharge down to about 20,” Buchmann says. “In that mid-range use, you get far more cycles than if you fully charged and discharged as we do on our cellphones.”

How do I enable optimized charging on my phone?

Optimized charging is a feature on most smartphones designed to protect their longterm battery health. And it does a few things. It slows down the charging of your smartphone when connected to power and it stops charging your smartphone when at full health, both of which are healthy for your smartphone’s battery. It can also delay charging your smartphone past 80-percent when, using AI, it predicts that your phone will be connected to power for an extended period of time (like at night); this way your phone stays in that “sweet spot” between 20-percent and 80-percent for longer.

To enable optimized charging on an iPhone (must be running iOS 13 or later): open Settings > select Battery > select Battery Health & Charging > turn on “Optimized Battery Charging.”

Is it bad to charge your phone multiple times a day?

No. Lithium-ion batteries like to be charged in short spurts, so plugging in for five-percent here and 10-percent there is not only fine, but advisable. Cycling your phone from 100 percent, down to zero, and back up has a very limited utility in that it can “recalibrate” a battery if it’s doing strange things like dying out of nowhere when it claims to be decently charged, says Buchmann. “But other than that, it’s not advised to fully cycle lithium-ion.”

Is using a fast charger bad for my phone’s battery?

Most new smartphones come with a feature called “fast charging,” which means that when paired with a compatible high-capacity wall adapter, they can get a high-percentage charge quite quickly.

You might be thinking that faster charging speeds, and the heat that comes from them, are bad for the overall health of your phone, but this isn’t the case. Degradation has more to do with the number of cycles your phone’s Lithium-ion battery goes through than how fast it completes each cycle. No matter what, a phone’s battery will degrade to about 80% percent after two years (or 500 completed charge cycles).

What’s the worst thing for my phone’s battery?

The worst thing for your phone’s battery health is to have it warm and fully charged at the same time. So get your phone off the charger when at 100-percent (or turn on its optimized charging feature).

The most stressful thing that can happen to your phone’s battery during regular use is not, in fact, being discharged, or even being empty. “The combination of full charge and warm actually causes more stress than usage,” Buchmann warns. “If you’re in a car in the summer, don’t put it on the dashboard. Put it on the floor, or in the shade.”

Circumstances where your phone or laptop are fully charged and extremely hot should be relatively rare and, as such, relatively avoidable. Don’t leave your fully-charged phone in the summer sun! Perhaps the most dangerous recurring heat-and-charge combination is a laptop that is always plugged in and prone to running hot, in which case investing in a cooling stand may be a smart move in case you ever want to use your laptop away from its tether.

Is it OK to use a wireless charger?

Using a wireless charger if fine for your phone’s battery life, especially if you maintain a charge that’s between 20-to-80 percent.

While lithium-ion batteries don’t like to be hot when they’re full, Buchmann says recent studies on vehicle batteries suggest they do like to be warm while they charge and discharge, so your wireless charger is probably not terrible for your battery’s health even though it may create additional heat. And if it helps you stay within the 20 to 80 percent power band, that’s a very good thing.

“For charging and discharging, the battery likes to be warm. Between 25 and 40 degrees Celsius (77-104 F),” Buchmann says. “But in storage, the battery should be cool, maybe 15 or 10 degrees Celsius (59-50 F).” Monitoring these temperatures constantly is a tall order and probably not feasible, but you can find apps that will take note of your batteries temperature and warn you if it hits extremes, which will at least help you avoid the worst scenarios.

Does it matter what kind of cable I use?

Pretty much every flagship smartphone supports wireless charging, but wired charging is still going to be faster. Android smartphones come with a USB-C charging port, which can charge really fast. The latest Samsung Galaxy smartphones (the Galaxy S23 Ultra, specifically) support fast charging at up to 45-watts, but that pails in comparison to other flagship smartphones by Xiaomi and OnePlus that support fast charging at more than 100-watts…which is faster than most iPhones.

For the last near-decade, every iPhone has come with a Lightning charging port, which charges significantly slower than USB-C — the last several iPhones have maxed out at 20-watts for fast-charging over a wired connection. You might be wondering if the iPhone 15 charges any faster because it’s the first iPhone to drop Lighting in favor of USB-C…but nope. The USB-C port on all iPhone 15 models, both Pro and non-Pro alike, has the same 20-watt max charging speed as the iPhone 14.

Can I fix my battery if it’s already bad?

If your phone’s battery isn’t great, the thing you can do before going about replacing it is to recalibrate it. This process does a “full cycle” — running your device’s battery from 100% down to zero in one fell swoop — to determine if it really is that bad. While this is not great a healthy battery’s long-term health, it can help provide a last gasp of clarity for a battery that’s going senile.

Apple has a specific recalibration process for this on iPhone. Barring that, you can attempt to recalibrate your battery by doing a “full cycle” and running your device from 100% down to zero in one fell swoop.

Replacing a battery is also an option. It’s not as simple as swapping in some new AAs, but Apple is running complementary replacement programs for certain Apple Watches and MacBooks that are suffering from battery woes. And in 2022, Apple will be launching a self-repair program, if you can hold out until then. Android phones, meanwhile, tend to be even more amenable to these repairs, though finding proper parts and instructions might be a bit more of a project.

Should I replace my battery instead of buying a new phone?

Most manufacturers offer repair programs or even self-repair programs that can replace the battery of your old device; as of April 2022, Apple has launched its first DIY repair program for iPhone. However, if you have a phone that’s several years old, it might be a better option to just buy a new one. Most older phones support the latest software updates, security patches and bug fixes.

If you’re considering replacing its battery, you need check to see how long the device’s manufacturer has promised to support your device with security updates and weigh that against your upgrade options. In many cases, your device might be pretty close to the end of its supported lifespan. On the bright side, that makes the decision to upgrade to new phone a no-brainer.

How much do I need to worry about my phone’s battery health?

It’s good to know the battery basics so you can avoid the worst pitfalls, but it’s also important to not fall into the trap of trying to be perfect. In the end, a lot of this is completely out of your hands. Despite the fact that lithium-ion batteries power a lot of our everyday life, the science of exactly how they function in practice is very much still in development, with new nuances still being uncovered. And much of the emerging science comes from tests on huge multi-cell vehicle batteries, which are similar but not identical to the single-cell battery in your phone. On top of that, your day-to-day charging usage experience is so riddled with variables that it’s pretty much impossible to confirm whether or not you’re doing things right.

But perhaps most importantly, your phone is not going to last forever, and not even super-humanly good battery treatment is going to change that. A screen replacement that’s just slightly too expensive to be worth it for your aging phone or outdated processor that can’t handle the latest software is all but destined to end your phone’s usable life even if the battery doesn’t. And until or unless the companies that make phones start designing them to survive a much, much longer lifespan, there’s not a whole lot you can do as the end user.

Just like your battery’s charge is a resource that you spend for the convenience of checking your phone, consider your battery’s overall lifespan as a resource you’ll need to spend wisely to preserve your own sanity. It’s up to you to decide what safeguards are worth the trouble.

“Why have a perfectly good battery when the glass is broken or the phone becomes obsolete?” Buchmann asks. “It all sort of harmonizes together to come to an end.” You’ll never prevent it, but armed with what you know now, maybe you’ll be able to postpone it a little bit longer.