Mac battery health: capacity, cycles and temperature

macOS gives you a health percentage and a cycle count, then stops. Those two numbers tell part of the story — and the first one is less trustworthy than it looks.

Maximum capacity

This is what your battery can still hold, divided by what it held when new. Health of 89% means roughly 89% of the original capacity is left. Apple’s own design target is that a battery keeps at least 80% after a thousand cycles.

It doesn’t fall smoothly. It sits still for weeks, then drops two points overnight. That’s not a fault — the number is an estimate from the battery controller, and the controller keeps refining its model as you charge.

Why two apps sometimes disagree

Because there are two numbers, not one. The raw value is measured maximum capacity over design capacity. The one macOS shows you is smoothed, so you don’t watch the estimate wobble.

So a point or two of difference between two apps isn’t a bug — one is reading the raw measurement, the other the smoothed value. Neither is lying to you.

The cycle count

One cycle means using 100% of the capacity, not plugging in once. Going 100% → 50% two days running counts as one cycle, not two. That’s why a desk-bound Mac can show very few cycles and still have degraded health: the cycle counter can’t see calendar aging.

Temperature, the number nobody checks

It’s the most actionable of the three. Lithium-ion degradation speeds up with heat, and charging a battery that’s already warm stacks both stresses on top of each other. Above roughly 40 °C (104 °F) at the cell, charging is better off paused.

macOS shows it nowhere. That’s one reason cell temperature sits right next to health in the free version of Cooked: without it, half the reasoning above simply can’t be done.

When to actually worry

• Health under 80% with few cycles: that battery has probably spent its life full and warm.
• Sudden shutdowns while charge is left: it can’t hold voltage under load anymore.
• Any swelling at all — a trackpad that’s risen, a case that won’t close: stop using the machine and get it looked at.
• Cell temperature sitting above 40 °C (104 °F) at idle: go find what’s running in the background.

The free version of Cooked shows health and live cell temperature right next to your charge limit, no account, no expiry. Cycles, power draw and the full history are in Pro.