Should I keep my laptop plugged in while I use it?
Q. Dear Umbra,
I work all day on a laptop (a MacBook Air). I’d like to prolong the life of my computer and battery so I don’t have the expense and waste of having to replace the laptop earlier than necessary. So what’s the best approach to plugging the laptop in vs. running it off the battery? When it’s 100-percent charged, should I unplug it and let the battery charge drop down low before plugging it in again? Or should I keep it plugged in all day long while I work?
Princeton, New Jersey
A. Dearest Jamal,
Most people understand that repurposing or recycling something is better than throwing it away. But you know what’s even better than that? Not recycling that thing, because it still works perfectly — or, at least, postponing that inevitable moment of mortality as long as possible. In our culture of planned obsolescence and gimme-that-hot-new-tech upgrades, this is a somewhat radical idea. I tip my hat to you, my status quo–shaking friend.
“Maintain it, don’t disdain it!” could be your creed. Apply it to most material things, but it’s particularly important with laptops and their lithium-ion batteries, as well as other electronics. Not only do these gadgets cost a pretty penny, but manufacturing them (and their batteries) requires water, energy, and rare-metal mining, and also brings up concerns about potentially toxic substances and human rights for miners. In short: The fewer you go through in your working life, the better.
To that end: There is indeed a plug-in protocol you can use to maximize your battery’s overall lifespan, Jamal, and it’s all about minimizing stress on that hardworking power pack.
The No. 1 thing that shortens a lithium-ion battery’s life? Letting it drain to zero. So try never to do that.
Why? Let’s start with a quick vocabulary primer. Depth of discharge refers to how much of a battery’s power has been used up: 40 percent depth of discharge means it has 60 percent of its life left, and 100 percent means you’ve let the battery run dry. A charge or discharge cycle is one full drop from 100-percent charged to dead as a doornail (or multiple partial discharges that add up to 100 percent). These two concepts are directly connected: The larger the average depth of discharge, the fewer total discharge cycles you get out of the battery.
In other words, if you regularly let that battery gauge dip into the red zone, then fully recharge it, the battery will degrade more quickly. And we’re not just talking a little difference: According to Battery University, an online juggernaut of battery information, if you tend to drain your battery low and then charge it back up to 100 percent, you’ll get about 300-500 discharge cycles before the battery starts losing capacity. But if you go with frequent partial recharges, you can boost total discharge cycles up as high as 4,700 before the battery’s performance starts slipping (and before you have to get much more aggressive about commandeering the outlet at the coffeehouse).
So is it best to just leave it plugged in at 100-percent charge all the time? Nope. As it happens, being completely full also stresses out a lithium-ion battery, aka the Goldilocks of portable power sources. The sweet spot, according to battery experts, is between 40 and 80 percent charged. In a perfect world, then, you’d drain the battery to 40, recharge it to 80, and repeat for years of top-notch battery performance. If monitoring your battery levels to this degree sounds a bit obsessive, well, it is. But unfortunately, I couldn’t find any easy apps or settings tweaks that would do this automatically for you. (Hey, developers: Opportunity alert!)
That said, it’s not a terrible practice to leave your laptop plugged in at times. You won’t “overcharge” a lithium-ion battery; once it tops up, the battery essentially steps off to the side and lets the power grid run the computer, waiting until you need it again. So while keeping the battery full does cause strain, it’s better than a 100-percent depth of discharge.
If you are tethered to the outlet for a while, some experts suggest removing your laptop’s battery entirely (though that’s not an option for Macs because they have integrated batteries). Removing it protects it from a lithium-ion battery’s No. 2 nemesis: heat. A battery’s optimal temperature zone is about 62 to 72 degrees (what a coincidence — that’s my optimal zone, too), and anything hotter than about 95 degrees can really wreak havoc. So keep your laptop out of hot cars, direct summer sunlight, Bikram yoga class, etc. And make sure to keep the cooling vents clear — work at a table or desk, not in bed with your computer on a quilt on your lap.
There you have the secret to long life: Watch your power levels, and keep it cool. And you know, I suspect following that advice might translate to a longer, happier life for ourselves as well as our batteries.