How to figure out if a MacBook power adapter or battery has gone bad

You plug in your adapter to your laptop, and the battery doesn’t charge reliably. Sometimes, your Mac dings to let you know it’s plugged in to power; other times, you have to plug and unplug, or even restart your computer. What’s up?

Battery charging involves three separate elements, so you have to go through a process of troubleshooting to identify which one is faulty.

The battery

For several releases of macOS, Apple has provided alerts and information about the health and status of a laptop’s battery. macOS warns you if something’s actively wrong with a battery when it determines this.

In macOS Catalina and earlier, you can Option-click the battery icon in the menu bar, and get a little more insight about the state of the battery. In macOS Big Sur, there’s a lot more detail about the battery available by default, but the condition is nested more deeply: go to the Battery preference pane, click Battery, and click Battery Health.

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Big Sur shows the current battery parameters, but not battery health. Click Battery Preferences for that.

The condition should be listed as Normal, but if the battery’s maximum capacity has dropped below a certain point (which Apple doesn’t specify), it might say Service Battery. You may also see one of a number of other messages that Apple doesn’t document, such as Service Recommended, Replace Soon, or Replace Now, all of which have a little more urgency, as the operating system has deemed the battery holds a charge poorly, or even not at all. If the battery dies entirely, an X appears through the battery icon, and the message reads No Battery Available.

In Big Sur through many earlier releases,  you can hold down the Option key and select  > System Information and click the Power item under Hardware in the left-hand navigation bar. Look for Condition there, where you can also see Cycle Count and, on certain models and versions of macOS, Maximum Capacity. The Cycle Count isn’t the number of times you’ve charged, but rather the total capacity of the battery divided by the total energy every used. The more cycles, the lower total capacity the battery has remaining, though it should be both years and hundreds of cycles before you see degradation below 80 percent. (A cycle measures 100 percent of the capacity discharged, not the time between being unplugged and plugged back in. If you deplete to 50 percent on two successive days and recharge to 100 percent, it counts as one cycle.)

In Big Sur, you can also use the Battery preference pane’s Usage History view to examine how and when your battery has been in use and when it’s been recharged. Starting in Big Sur, Apple automatically throttles and adjusts your charging pattern to reduce stressing the battery: it no longer charges the battery to 100 percent at all times, but based on your usage, keeps it at 80 percent whenever possible. Lithium-ion batteries face additional wear when fully charged all the time, which reduces battery life. This chart may reveal a pattern of slow failure.

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Usage History in Big Sur reveals the pattern of charging on your laptop.

The adapter

It’s natural to look at your power adapter for signs of wear, like a crushed portion, fraying cable insulation, bent or marked AC plug blades, dirty or bent parts of the laptop connector, or other signs of problems. However, a frequently used adapter may look fine to the eye, but the internal wiring or circuitry and components in the power conversion part that handles AC-to-DC transformation could be on their way out.