At one point or another, all laptop users find themselves pondering the same question: is it bad to leave your laptop plugged in all the time?

Turns out, the answer isn't entirely straightforward. So let's take a look.

Know Your Laptop Battery

There are two main types of batteries used in laptops: lithium-ion and lithium-polymer. Although they are different technologies, they function in broadly the same way, generating power through the movement of electrons. This constant flow is also needed to help keep the battery healthy.

For both types of batteries, the following statements are true (at least as far as modern laptops are concerned):

  • A battery cannot be overcharged. There's no danger of overcharging a battery if you leave it plugged in all the time, even 24/7. As soon as it hits 100%, it will cease charging and won't start again until the voltage falls below a certain level.
  • Fully discharging a battery will damage it. Allowing the battery to become completely empty for an extended period can put it into a deep discharge state. This can be fatal—you might never be able to charge it again. (You can try these methods to jump-start a dead laptop battery.)

So, based on this, do we conclude that you should leave your laptop plugged in all the time? Not quite.

Things That Damage Lithium Batteries

The truth about lithium-based batteries is that they are inherently unstable. They begin to lose capacity from the moment they are produced, and numerous factors hasten their decline. These include:

  • Charge/discharge cycles: Every battery has a finite number of times it can be charged and discharged.
  • Voltage level: The higher the charge level (measured in volts per cell), the shorter the battery's life.
  • High temperature: Temperatures over 30 degrees Celsius or 86 degrees Fahrenheit can cause irreparable damage.

The last two points are the ones that we're most concerned with here. A comprehensive study by Battery University highlights how voltage levels and high temperatures will shorten the life of a battery in isolation—and even more when they combine.

Charge or Voltage Level

Lithium-ion batteries charge to 4.20 volts per cell, which amounts to 100% of their capacity. At this level, the battery will have a lifespan of 300-500 discharge cycles.

how charge level affects battery capacity
Image Credit: Battery University

Every 0.10V/cell reduction in the charge doubles the number of discharge cycles until the optimum level is reached: 3.90V/cell, with 2400-4000 discharge cycles. Unfortunately, at this level, the battery is only around 60% charged. The runtime will be a little more than half of a fully charged battery.

Heat

And then there's heat. High temperatures, typically classified as being over 30 degrees Celsius, will shorten the life of a battery irrespective of any other factors. Simply leaving your laptop in your car on a summer afternoon is a bad idea.

When you combine the stress of high temperature with the stress of high voltage, the effects are even worse. The Battery University study shows that a battery stored with a 40% charge at 40 degrees Celsius would see its capacity fall to 85% after a year.

how heat affects battery capacity
Image Credit: Battery University

Charged to 100%, the capacity falls to 65% under the same conditions. For a fully charged battery at 60 degrees, the capacity plummets to 60% in just three months.

The evidence seems clear. Keeping the battery permanently charged at 100% will slowly shorten its life. Keeping it at 100% and exposing it to high temperatures will shorten it much quicker.

And remember, these high temperatures are not just environmental. Resource-intensive tasks such as gaming or video editing will considerably increase heat levels, and using the laptop on a pillow or in a poorly designed case will trap that heat as well.

For the sake of your battery, it's always a good idea to fix an overheating laptop.

Should You Keep Your Laptop Plugged In?

Does leaving your laptop plugged in ruin the battery? Yes, it does. But then so does charging it every day.

Microsoft clearly states that it's not okay to keep a laptop plugged in when it's fully charged, because "keeping the battery charged to 100% all the time can cause it to deteriorate faster." Apple's advice is no longer on its website, but you can still read it on the Internet Archive. The company recommended against leaving a laptop plugged in all the time, suggesting:

"An ideal user would be a commuter who uses her notebook on the train, then plugs it in at the office to charge. This keeps the battery juices flowing..."

Increasingly, though, you don't need to worry about it. macOS now comes with an Optimized Battery Charging setting that charges your MacBook to 80% when you keep it plugged in and only tops up the rest when it thinks you need it.

mac optimised battery charging

Windows 11 also has a Smart Charging feature that works in a similar way, although it's up to each laptop manufacturer as to whether and how they implement it. But if you see that your laptop is only charging to 80% when you use it, this is not a bug. It will help extend the lifespan of your battery.

Should You Remove the Battery?

Finally, should you remove the battery altogether when using your laptop on AC power? It's a less relevant question than it once was because most laptops now have sealed batteries.

Where they are replaceable, the answer seems to vary from one manufacturer to the next. Acer, for instance, says you don't have to remove the battery on AC power, but should remove it if you aren't going to use it for several days. Apple's advice from when it produced laptops with removable batteries (via the Internet Archive) was to never take them out.

It all comes down to the power management setup in the laptop. Some may reduce the power when a battery isn't present, just as some do when the battery level gets low. This could leave you with subpar performance.

If you do choose to remove the battery, ensure that you store it properly. This usually means being charged between 40% and 80% and kept at room temperature.

Is It Bad to Keep Your Laptop Plugged In?

Leaving your laptop plugged in will not cause short-term damage, but if you only ever use it on AC power, you'll almost certainly find that after a year, the battery's capacity has been significantly reduced. Similarly, if you only ever use it on battery power, you'll get through the battery's discharge cycles quicker.

So, even allowing for smarter software that tries to limit the damage, the best solution is something of a compromise: use it on battery power some days, and keep it plugged in on others. And whatever you do, make sure the battery doesn't get too hot.