Where the adapter's watts go

Updated 23 August 2026 · quoted wordings are the app's own strings. Who measures this.

Plugged in, the interesting question changes. Not "what is draining the battery" but "is the charger keeping up". The app splits the adapter's output four ways: what it delivers, what the machine eats, what reaches the battery, and what is left spare.

When the charger cannot keep up

A laptop under load can want more than its adapter supplies, and then the battery quietly makes up the difference while the cable is still plugged in, which is how you end up watching the percentage fall with the charger attached. It reads like a fault. It is not one.

When that happens the app names the shortfall in watts and points at the hungriest running app. That pairing matters: a number alone tells you the charger is small, the pair tells you whether the charger is small or the workload is large.

Four ways it declines to answer

Charging is the state where a measurement is easiest to get wrong, so most of the logic here is about not blaming the wrong thing.

Situation	What the app says
Cable just plugged in	"Plugged in, working out the charge" — and the time-to-full estimate stays hidden until the meters describe this power source
Nothing measurable arriving	"The adapter is not giving anything measurable yet — a display negotiates power for a while. If this stays, try another cable or port."
Shortfall real, culprit unclear	"The Mac needs more than the adapter delivers. Until the two meters agree on how much, naming an app would be a guess."
The two meters disagree badly	The shortfall is not printed at all rather than printed wrong

The second row is worth reading twice. It is the case that most often looks like a broken cable or a dead port, when in fact a display on the other end of it is still negotiating how much power it will pass through, and during that negotiation the honest answer is that nothing measurable has arrived yet.

What this does not do

There is no history of adapter watts, and it is not on a list to add. While the Mac is on mains, the app does not accumulate energy windows at all: this measurement lives in memory and goes stale within a couple of minutes. A chart of what the charger delivered today would have to be assembled from data that was never kept.

No row carries minutes while plugged in. Minutes describe what an app took out of the battery, and on mains the battery is not paying. The list is still there, the numbers are still watts, but the gain column is empty by design.

It does not measure while nothing is open. The full pass over processes runs only while the popup or the statistics window is on screen.

Questions people ask

My Mac discharges while plugged in. Is the battery failing?

Usually not. Under heavy load a machine can draw more than its adapter provides, and the battery covers the difference. The number to look at is the shortfall, not the percentage.

Does a bigger charger charge faster?

Only up to what the Mac will accept, and only when there is spare capacity after the machine's own draw. If the shortfall is zero and there are watts to spare, a larger adapter changes nothing.

Why does it say "working out the charge" instead of showing numbers?

Because the meters need to describe the current power source before their readings mean anything. Showing the previous source's figures for a few seconds would be worse than showing nothing.

Charging stopped at 80% — is that this?

No, that is a different message with different causes. The charge controller records why it stopped, and one command reads it.