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

You don't have to think too hard about preserving your smartphone's battery - especially overnight.

For years, the myth has persisted that plugging your smartphone in a charger while you sleep will cause some sort of harm to that phone's battery. Though many people do it anyway, others warn that if you continue to charge a phone that is already fully charged, you'll waste away 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."

By "cycle count," Wiens is referring to 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 in total, 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 to begin with.

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. That's a process that begins as soon as you start using your phone, and there's little you can do to stop it.

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

That's because modern smartphones are built in a way that prevents them from taking in too much more current than is necessary once they're fully charged. In other words, they know when to take it easy.

"Smartphones, as the name would suggest, are smart," said the Anker spokesperson. "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 of charging overnight being harmful - or causing 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."

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 complaint he sees with regard to smartphone battery life is people saying their device either won't charge above a certain point, or 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.