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Is it a bad idea to leave your smartphone plugged in overnight? At a time when the smartphone is basically an extension of self, this is surely one of the most relevant questions we could ask.

We’ve all done it: Just before bed, you plug your smartphone into its charger so that it can get a full charge while you sleep through the night. The idea is to wake for the day with 100 percent charge on your smartphone’s battery. But then you heard that charging your phone overnight damages the battery and eats away at its capacity over time, so you turn to Google for answers.

So before we get into the nitty gritty details of this overnight charging myth, we’ll give you the short answer first. Yes, you can leave your phone plugged in overnight. This wasn’t always the case, though, so be sure to read on to find out the truth behind this old advice. We’ve also attached some charging do’s and don’ts at the end to help you make your smartphone battery last longer.

6 common battery myths you probably believe

Lithium versus nickel

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You’re probably aware that the majority of today’s tech runs on lithium ion batteries. Years ago, batteries were primarily made of nickel like the Duracell and Energizer batteries you buy in stores. Nickel-based batteries exhibited a tendency to have a cyclic memory. If they weren’t given full charges in between cycles, they might “forget” their full capacity and remember the point to which they were last charged as being the maximum capacity. Many of us have never used nickel-based batteries in our mobile devices since the transition to lithium ion had occurred by the early 2000s.

Lithium ion and nickel batteries have a few major differences
Fortunately, lithium-based batteries didn’t suffer from the memory phenomenon often exhibited by the nickel batteries. Lithium batteries played a major part in the mobile phone revolution. For one thing, they’re able to hold a lot of power while remaining fairly compact, which allowed mobile phones to become increasingly small and thin. Also, lithium batteries have a much better lifespan and recharge fairly quickly. The one caveat is temperature sensitivity.

Heat: The Silent (Battery) Killer

Lithium Ion Batteries AA

Now we get to the most significant threat to your lithium-ion or lithium-polymer battery, which is heat. Granted, batteries dislike the cold just about as much as they dislike the heat, but the latter is more relevant when it comes to leaving your device plugged into its charger overnight.

The charging temperature for lithium-based batteries — i.e., the temperature at which a battery is capable of receiving a charge — is 32° to 113℉. Meanwhile, lithium-based batteries can discharge at temperatures as low as -4℉. Fast-charging technologies work best at warmer temperatures between 41° and 113℉, with no charge capable of occurring when the temperature is lower than 32℉.

There are a couple important things that these figures tell us. First, a lithium-based battery can discharge at temperatures far below freezing, so keeping them in your kitchen freezer won’t prevent them from self-discharging. Second, a lithium ion battery warms up as it charges. As it gets warmer, it charges faster. But since a battery can’t hold more than its capacity, after reaching a full charge the battery expends the excess power by giving it off as heat. Overnight charging becomes a problem when a battery has no way to reroute the incoming current after reaching its capacity.

Fortunately, there’s a solution to this problem.

Smartphones use battery power smartly


Batteries used in mobile devices today are still mostly the same as they have been for almost two decades, but the devices that they power have become much, much smarter. Nowadays we have less to worry about when it comes to the battery health because power optimization has been put on the shoulders of the software running these devices.

Thus, we get to the answer of our main question: Should we leave our smartphones plugged in overnight? The answer to this question is a resounding sure, why not?

Our mobile devices have gotten much smarter over the years
As we discussed above, the main danger in leaving your smartphone plugged in overnight was allowing the battery of your device to get hot and remain hot through the rest of the night. However, our mobile devices have gotten much smarter. They can stop charging when the battery has reached its full capacity and begin using the connected charger as its primary power source, allowing you to wake up to a fully-charged battery while your phone remains powered on through the night. It’s a pretty sweet deal.

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However, that’s not to say that your charging habits can’t have an effect on the health and longevity of your battery. While you’re not at risk of overheating your battery by leaving your phone plugged in overnight, we’ll still walk you though a number of tips you can incorporate into your charging habits to keep your device’s battery in tip-top shape.

Smartphone battery charging best practices

  1. Each lithium-based battery is capable of a finite number of charge-and-discharge cycles. With each cycle, the capacity of the battery is very slightly reduced, so we want to avoid as many complete cycles as we can. To do this, try to keep your battery’s charge level between 40 percent and 80 percent power. Of course, this won’t always be possible, but try not to let your phone’s battery level get below 40 percent too often and keep the number of complete top-offs to a minimum.
  2. Try not to use fast charge every single time you charge your phone. Most fast or rapid charge systems cause the battery to become hot, which we now know is bad for your battery. If you’re using the fast charge option every single time, the battery is getting excess heat more often than it should, resulting in a shorter lifespan.
  3. Earlier in this discussion, we mentioned how lithium ion batteries don’t suffer from the same cyclic memory of nickel-based batteries. While that’s true, the internal power meter in your smartphone — the part that determines the battery’s current power level — can sometimes get thrown off. You can recalibrate by doing a full discharge-and-charge cycle: Use your phone until it dies. Once it’s dead, charge it to full capacity while leaving its power off. Finally, power your phone back on and make sure it reads as fully charged; if it doesn’t, power off and continue charging. Repeat this process once a month or so to make sure your battery is functioning optimally.

Wrapping up

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The battery is one of a smartphone’s most important components; after all, a smartphone with a dead battery is little more than a paperweight. So it goes without saying that we surely don’t want to do anything that would damage our batteries and make them less efficient. Although there are some who still believe it’s a bad idea to leave your phone plugged in overnight, all signs point to overnight charging being a completely valid way to make sure you start your day with a full charge on your smartphone.

What do you think about overnight charging? Have you ever noticed a difference in the capacity of your device’s battery after charging overnight? Do you agree or disagree with our findings? Sound off in the comments below with your thoughts.