We have all read it multiple times, and in multiple places that it’s not right to charge one’s phone overnight, but while we like to ignore the warning, the truth is that it actually is a dangerous thing to try.
Mobile phones contain a rechargeable lithium-ion (or li-ion) battery. Li-ion batteries charge faster than traditional rechargeable batteries. That’s why you can plug your iPhone or Android phone into a charger, and revving it up to at least an 80% charge happens fairly quickly. But as we all know, our smartphone battery charges don’t last long. We’re often lucky to get through the day without our phones losing all their juice.
Part of that dilemma is because the batteries on our phones are relatively small and can hold only so much capacity. But the other part is due to the way we use our phones. Constantly checking email, texting people, listening to music, watching videos, using apps, playing games – all those activities eat up a single charge, causing our phone batteries to run out of gas, often sooner than expected.
For that reason, many people (myself included) probably charge their phones overnight. You then wake up to a 100% freshly charged phone in the morning when you have to trot off to work or otherwise start your day. In most cases, your phone probably needs only an hour or two to hit 100%. Leaving it plugged in longer is pointless. So what happens if you act as I assume most do, and leave your phone plugged in overnight?
The good news is that you can’t overcharge your phone’s battery, so don’t worry about that. Your phone stops drawing current from the charger once it reaches 100%, according to electronics experts.
So what’s the not-so-good news?
Even though a charger turns off the juice when your phone reaches 100%, the charger will continue to top off the charge during the night. Such a “trickle charge” attempts to keep it at 100% to compensate for the small bit of charge that your phone just naturally loses on its own. So your phone is constantly being bounced between a full charge and a bit below a full charge. These trickle charges can lead to higher ambient temperatures for your phone, which can reduce capacity over time.
Li-ion does not need to be fully charged as is the case with lead acid, nor is it desirable to do so.
Rechargeable batteries are also basically doomed from the start. Batteries in mobile devices are in constant decay from the moment they’re first used. This results in a gradual loss of their capacity, or ability to hold a charge. That’s why those who’ve owned a phone for more than a couple of years tend to find that their battery loses its charge quicker than just after purchase.
By keeping your phone charged overnight, you’re actually increasing the amount of time your device spends with the charger, thereby degrading its capacity that much sooner.
If you think about it, charging your phone while you’re sleeping results in the phone being on the charger for 3-4 months a year. So even though the manufacturers try their best to cover this scenario, this process inevitably lowers the capacity of your phone’s battery.
What charging advice do experts have for smartphone owners?
Don’t wait until your phone gets close to a 0% battery charge until you recharge it. Full discharges wear out the battery sooner than do partial discharges. It is recommended that you wait until your phone gets down to around a 35% or 40% charge and then plug it into a charger. That will help preserve the capacity of the battery. You should also keep your phone cool, as higher temperatures accelerate the loss of battery capacity. Pro tip: Take off your phone’s case before you charge it.
The moral of the story? The loss of capacity generally doesn’t become noticeable until after the second year. If you replace your phone every year or two, then don’t sweat the overnight charging since you’ll have a new phone before the battery in your old one starts to conk out. But if you hang onto your phone for more than a couple of years, resist the urge to charge it overnight, and your battery will retain its capacity that much longer.