Yes, it's safe to leave your smartphone plugged into the charger overnight

For years, the myth has persisted that plugging your smartphone in to charge while you sleep will harm the phone's battery. Though many people do it anyway, others warn that charging a phone that is already fully charged will waste its battery's capacity.

But while those fears may have made sense with the batteries of years ago, they're overblown today.

"Having your phone plugged in at night doesn't diminish the battery," says Kyle Wiens, the head of iFixit, a California company known for its repair guides and "teardowns" of consumer gadgets. "It's all about cycle count — it's all about how you actually use the battery, how much work you're making the battery do."

The cycle count is the number of full charges a smartphone can deal with before its battery is significantly degraded. For instance, if you drain a phone's battery halfway then recharge that half-empty capacity, that takes up half a cycle.

Wiens says the typical smartphone battery will get about 400 charge cycles, which should help the device last at least a year and a half. It's not uncommon for some to last beyond that. That's about as long as many people keep their devices anyway.

But leaving your phone in the charger overnight, even when it's fully charged, won't do much to change how frequently its battery runs through cycles, which are affected by use of the phone.

"In terms of the gradual erosion of battery life, what must be understood is that phone batteries are constantly in a state of decay," a representative for the battery and charger accessories maker Anker says. "Sleeping with a phone charging overnight will make no noticeable difference in the process."

That's because modern smartphones are designed to avoid taking in more current than is necessary to fully charge them. In other words, they know when to take it easy.

"Smartphones, as the name would suggest, are smart," the Anker representative said. "Every unit has a built-in chip that will prevent charging once 100% capacity has been reached. Therefore, provided that the phone in question is purchased from a verified and legitimate retailer, there should be no danger in leaving the phone charging overnight."

The idea that charging overnight may be harmful — or cause a series of "mini-charges" that continuously drain the battery — typically comes from people's experiences with older tech, Wiens says.

"I think what gives people this feeling is that back in the day some phones or some laptops would go back and forth between 99% and 100%" on their battery indicators, he says. "That had more to do with measuring errors of what the software was showing you more than anything else."

But one danger that may exist with leaving your smartphone plugged in overnight is temperature. As Apple warns on its website, the lithium-based batteries used in modern smartphones can be degraded by extreme heat — though that's something to watch out for regardless of when you recharge your device.

Wiens says the most common complaints he sees with regard to smartphone battery life are people saying their device won't charge above a certain point or will die out at a percentage above zero.

Those suffering from this may just need to get a replacement battery, Wiens says, but they could also try discharging their device all the way down to 0% then filling it back up again. This will effectively "recalibrate" the battery's internal counter; Nintendo recently suggested a similar method to fix a battery issue on its Switch console.

Either way, problems like that go beyond charging your phone overnight. If your battery is running low just before bedtime, know that you can rest easy until the morning.

Yes, it's safe to leave your smartphone plugged into the charger overnight

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