Your Mac reports two battery health numbers

Updated 15 August 2026 · every figure below was read from one Apple silicon MacBook Pro at 533 cycles, and the section at the bottom says exactly how far that generalises

System Settings tells you the battery is at 87%. You open a battery app and it says 85%. Neither is lying and neither is guessing — they are reading two different numbers out of the same chip, and the battery controller publishes both.

The two numbers, measured

The controller reports a design capacity — what the pack held when it was new — and then two views of what it holds today. On the Mac used for this page:

The two are 152 mAh apart, about 2.4 percentage points. System Settings showed 87% at that moment; WattMate showed 85%.

So the disagreement isn't a bug in either one. It is a choice of which of two published numbers to print, made differently by different software.

Why there are two at all

A battery's capacity isn't a fixed quantity you can look up — it is something the controller estimates, and the estimate moves with temperature, with how full the pack is, and with how recently it was charged.

The declared figure is that estimate after smoothing: stable, slow to change, meant for a label that says "your battery is fine". The raw figure is the estimate as taken: closer to what the pack will actually give you today, and noisier for exactly the same reason.

Watch it move. Two readings forty minutes apart on the same Mac, while the charge fell from 56% to 32%:

Both moved by the same 62 mAh — about a percentage point — and the gap between them did not change by a hundredth. Three readings twenty seconds apart did not move at all. That tells you two things: the numbers drift over a day, and the difference between them is not drift. They are two quantities, not two measurements of one.

Which number should you use?

It depends on the question, and the questions are genuinely different.

• "Is my battery healthy enough, should I replace it?" — the declared figure. It is stable, it is what Apple support will discuss with you, and it is the one that matters for a warranty conversation.
• "How much charge do I actually have to spend today?" — the raw figure. That is what the pack is working with right now, and it is what any honest estimate of remaining time has to be built on.

WattMate shows the raw figure, because everything else it prints is measured energy — watts, watt-hours, minutes — and those have to be built on the same pack the measurements came from. Printing a smoothed capacity beside measured energy would quietly break the arithmetic that connects them.

And because that means disagreeing with System Settings, the app now says so itself, on the same screen, rather than leaving you to discover it: it prints Apple's figure next to its own and names the difference.

What this does not explain

A gap of two or three points is normal and expected. A gap between health and how long the Mac actually lasts is a different problem with a different cause — a battery at 90% can still give you three hours if something is holding the machine awake or drawing hard in the background. If that is your question, the answer is not in the capacity number at all: battery health says 96% but it only lasts four hours takes that one apart.

Questions people ask

Which app is telling the truth?

Both, if they say which number they are showing. The failure isn't picking one key over the other — it is printing a percentage with no statement of what it is a percentage of.

Why does the number change during the day?

Because it is an estimate that moves with charge level and temperature. On the Mac measured here it moved a full percentage point in forty minutes. An app that shows the raw figure without smoothing will show that wandering; one that only ever lets the number fall — as WattMate does — will hide the rebounds and keep the history honest about wear.

Is a two-point gap a sign of a failing battery?

No. Both figures came from the same healthy pack, reported by macOS as being in Normal condition, on the same second.

Should I worry when it drops below 80%?

80% is the capacity Apple designs the pack to still hold after its rated cycle count — a design target, not a failure threshold. A battery below it works; it just holds less.

How far these numbers generalise

Honestly: not very far, and it would be easy to pretend otherwise. Every figure on this page came from one Mac, at 533 cycles, on 15 August 2026. The 152 mAh gap is a property of that pack and that moment — your own gap will be a different size, and it can be smaller or larger.

What does generalise is the mechanism: there are two published capacity numbers, they differ, and software picks one. We are now recording both figures side by side on every machine that runs WattMate, so that within a month this page can say whether the gap looks the same across different packs instead of guessing from one.

Related: health is fine but the Mac dies early · how we count everything else · why charging says "on hold"