Q: I like to charge my phone overnight while I'm sleeping. It really only takes a couple hours to charge the phone, so this worries me. I have heard that charging a battery too long can shorten its lifespan. Is this true?
A: There’s a lot of contradictory advice about batteries out there. The reason for this is because there are a lot of different types of batteries, and different types require different care. A similar thing that I had heard was that if you unplugged them before they were finished charging, you would reduce their charging capacity. That was pretty worrying to me because sometimes I need to grab my phone and go, whether it’s done charging or not. Was this killing my battery?
Fortunately, neither of us needs to worry. You see, virtually all modern smart phones use lithium-ion batteries. These batteries are designed with the understanding that you’re going to be using your cellphone on the go. Sometimes you’ll need to unplug before you’re finished charging; sometimes you’ll plug in the phone for a quick top-off, and, of course, you'll often leave it plugged in overnight. These batteries are designed for all of that.
And it’s also OK to recharge your battery before it runs all the way down. In fact, for lithium-ion batteries, it’s preferable. Maybe once a month or so, let your battery run all the way down before charging it. This will help calibrate the battery. But most of the time you don’t need to do this.
The truth is, the major threat to your battery life is time. Rechargeable batteries have something known as "charge cycles." A charge cycle is basically going from near-empty to completely full. Every phone battery has a finite number of charge cycles. That number is very large, but eventually your phone’s battery will reach a point where its charging capacity starts getting smaller. Rechargeable batteries just don’t last forever.
Now, going back to your original question, fortunately all smart phones these days are programmed to stop charging the battery once the battery is fully charged, and from that point on, the phone runs solely off of the charger's electricity. So, there's no risk of it overcharging the battery when you leave it plugged in overnight. When I’m at work, I usually leave my phone plugged in at my desk. When the battery is fully charged, the battery isn’t in use at all, which should extend the lifespan of the battery.
You can also help prolong your battery’s lifespan by using fewer charge cycles. That means, of course, using less battery power. Conserve battery use by dimming your phone’s screen, turning off 3G/4G data when you have very few or no cell bars, and not playing too many games. Games, especially ones that have intense graphics, like fighting games and racing games, tend to eat up batteries like crazy.
Another thing that is bad for batteries is heat. Using your cellphone in a hot environment can run down the battery really fast. And of course your phone can heat up as well from intensive use. Try to avoid that, or at least not run apps that heat up your phone for too long. A cool phone is a happy phone.
Now, it’s important to keep in mind that we’re talking lithium-ion batteries here. Most cellphones, tablets and laptops use lithium-ion batteries, but many other devices do not. So, care for them may be different.