Battery replacement

A battery loses capacity while it is being used. That is not a fault — it is how lithium-ion behaves. The question is not whether capacity falls but when the fall starts costing you a working day. You can look that number up yourself in ten seconds, and below is both how and what the number means.

How we read the percentage

90–100%As new. The machine lasts what it was sold to last.
80–90%Normal wear. Most machines still manage a working day.
70–80%You notice it. Plan a replacement, though it is rarely urgent.
Under 70%Replace it. Below this the machine is effectively tied to a socket.

That is how we read the number — not an official standard. Capacity is only half of it: how long a machine actually lasts also depends on screen brightness, what is running, and which machine it is. Two machines at 85% will not necessarily last the same time.

How to check it yourself

Windows

01Open Command Prompt or PowerShell.
02Type powercfg /batteryreport and press Enter.
03Open the HTML file whose path the command prints.
04Find DESIGN CAPACITY and FULL CHARGE CAPACITY. The second divided by the first is the battery's health as a percentage. The report also shows CYCLE COUNT — the number of full charges.

Mac

01Open System Settings and choose Battery.
02Click the ⓘ next to Battery Health. The maximum capacity is shown there as a percentage.
03Hold Option and click the Apple menu → System Information → Power to see the cycle count.

What we do

We measure the actual capacity as a percentage of new before suggesting anything.
We replace the battery and check that the machine charges and discharges correctly afterwards.
We take the old battery away for correct disposal if you want it gone.

What we need

The machine's model — usually on the underside or in the system information.
The battery percentage, if you have looked it up. Then we can say whether a replacement is worth it at all.