You may already have heard the warnings: Don’t overcharge your mobile phone. Make sure you unplug it from the charger after it reaches 100%. Don’t leave it charging overnight. Or else
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
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
Rechargeable batteries are also basically doomed from the start. Batteries in mobile devices are in constant decay from the moment they’re first used, says Campos. This results in a gradual loss of their capacity, or ability to hold a charge. That’s why those who’ve owned a phone more than a couple of years tend to find that their battery loses its charge quicker than just after purchase. I’ve owned my current iPhone 6 for almost three years and have seen a significant drop in capacity, especially over the past few months. Charging and recharging the battery doesn’t help. An Apple webpage about batteries cautions that the capacity diminishes after a certain amount of recharging, and that the capacity on li-on batteries diminishes slightly with each charging cycle.
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.