Should You Leave Your Phone Charging Overnight?

You may have heard that leaving your smartphone charging overnight—either plugged in or atop a wireless charger—can damage your battery.

But is it actually harmful or dangerous to do that? Or is this one of those persistent phone battery myths that refuses to go away?

The simplest and most straightforward answer, according to most experts, is that you can leave your smartphone charging all night as long as you are aware of some limitations and details.

The practice of leaving your phone to juice up through the night is not as problematic as it used to be. Starting in 2010, manufacturers have made it customary to integrate power management chips into their designs that choke the power coming in when the battery reaches 100 percent. The first such chips—called power management integrated circuits, or PMICs—began to peep out from the mid-2000s but became standard in phones somewhat later.

When integrated into a motherboard, the PMIC manages things like battery charging, the system’s sleep, wake, and power cycle events, and the voltage and current used by the display, processor, memory, and other components. It optimizes all of these things to reduce the overall power consumption and extend the device’s battery life. These chips also prevent phones from overheating too much, and they consequently reduce the fire risk to near zero.

It can’t do all of that by itself, though. You still need to take care of your battery. The best way to keep batteries from incurring too much wear is to keep the cell charged between about 30 percent and 80 percent. Doing this reduces the thermal and chemical stress on the lithium-ion cells. Apply common sense to this advice; don’t always just recharge every night, but mix in some more controlled daytime charging to keep the battery healthy.

And while leaving the phone charging all night is not a problem, it would be good to pay attention to where that charging is taking place. Leaving the phone under blankets, pillows, or near other heat sources increases the temperature and can accelerate battery degradation.

Tips for “Defensive” Charging

The phone’s PMIC can really only function properly if you use the phone’s original charger or a certified replacement. If you plug into a cheap power supply you bought from an untrusted source, the chip may not be able to perform all of its safety checks.

Specifically, only use chargers with the proper safety certifications. In Europe, the product should have the CE marking, which is a basic requirement to market power supplies in the European Union. In North America, look for the UL mark, which is a third-party safety certification check carried out by Underwriters Laboratories.

Also, make sure the numbers match up. A charger capable of outputting 18 to 30 watts can provide fast charging for most phones, and some newer phones can benefit from a high-end charger of 45 to 65 watts for even faster charging. Check your phone to see what’s compatible. Always avoid older chargers offering low power like 1 or 2 amps or less than 5 watts, as well as models with exceedingly high power ratings of 140 to 240 watts, unless your smartphone explicitly supports them, such as the Motorola Edge 40 Pro, which is capable of 125-watt wired charging. Mainstream phones from Samsung and Apple work at much lower thresholds.

We also suggest turning on “optimized charging” features in iOS and Android if you haven’t already. This will slow down or postpone overnight charging to keep the phone between 80 and 90 percent for most of the night, only allowing the battery to go all the way to 100 percent toward the time you typically get up in the morning.

It’s even better for your battery’s health if you have the option to unplug the phone when it gets just above 90 percent. This becomes more important if your phone is more than just a couple of years old, since devices tend to heat up more during charging as they get older.

This story was originally published by WIRED Italia and has been translated from Italian.