Batteries aren’t magic. They’re chemical. And, like most things built by humans, they wear down over time. I don’t need to tell you this—anyone who has owned a MacBook knows that battery life gets worse and worse as it ages. But what if I told you it’s possible to slow that process down?

One common bit of advice is to only charge your devices up to 80 percent most of the time. Battery University, funded by a consultancy that helps large companies get more out of batteries, suggests this based on its research. So does the National Renewable Energy Laboratory.

But how do you actually follow this advice? The good news is that your MacBook already does this, sort of, and there’s a great free application that allows you to go even further.

Built-In Optimization

Your Mac is designed to only charge up to 80 percent—at least, under some circumstances. By default, Mac devices learn your charging and usage routines and juice up your battery based on that. According to Apple, “Your Mac delays charging past 80 percent when it predicts that you’ll be plugged in for an extended period of time, and aims to fully charge the battery before you unplug.”

What does this mean? Well, for example, if you tend to charge your laptop overnight, your Mac will charge up to 80 percent, then wait until morning to top off the last 20 percent. The idea is to minimize the amount of time the battery is fully charged in a way that you won’t even notice.

The nice thing about this feature is that you don’t have to do anything to look out for your battery’s health. Your Mac is already doing what it can to only charge up to 80 percent whenever your routine suggests it won’t affect you.

(This feature is actually a macOS setting that’s toggled on by default. You can find it in Settings > Battery > Battery Health, where you can toggle this protective setting off, though you should keep reading to figure out if that’s best.)

If you’d rather not think about how charged your battery is, ever again, stop reading. If you want more control, though, I have some advice.

Take Control With a Free App

There are a few potential issues with Apple’s approach. The first is that you’re not in control. You might, for example, discover your MacBook isn’t fully charged if you wake up earlier than usual to catch a flight, and then you’re stuck with a partially charged battery on a long travel day.

For me, though, the bigger issue is that my daily battery usage just isn’t very routine. I do a lot of my work at my desk, where my computer is plugged into my monitor, which also charges it. I like to move around my space throughout the day, though, which means I’m unplugging at random times. And sometimes I put my laptop in my bag and work at the library or a coffee shop. It would be nice to be able to make sure I’m fully charged when I do that.

You get the idea: Not everyone’s routines are predictable. If this sounds familiar, and you’d like to take direct control of your MacBook charging, I recommend the free and open source app named Battery.

This application lives in your menu bar and forces your laptop to only charge up to 80 percent. You can allow full charging at any time, though, by clicking the menu bar icon.

This is going to require a bit of planning and attention on your part. You’re going to have to remember to enable a full charge before you need it, and then turn the limit back on when you know you won’t need it.

But for someone like me, who mostly uses their MacBook at their desk, it feels like a way to ensure my battery stays healthy as long as possible.