Battery Health Estimator

Work out your battery’s real health from its capacity figures.

What you provide

Design capacity(mAh or Wh)

Full-charge capacity(same unit)

Result

PASS

Battery at 84% of its original capacity

Above 80% is considered healthy. Some wear is normal and expected; there is nothing to act on here.

Capacity remaining

84.0%pass

Below 50% — significantly degraded
50–80% — noticeable wear
Above 80% — healthy

Measured against the design capacity you entered, not against a new battery of the same model.

Diagnostic telemetry

Health: 84.0%
Wear: 16.0%
Design capacity: 5000
Full-charge capacity: 4200

What this cannot tell you

A browser cannot read your battery. These figures come from your own system report — this tool only does the arithmetic on what you supply.
Both capacities must be in the same unit (mAh or Wh). If they are swapped or mixed, the result is meaningless.
Capacity is one measure of health. A battery can also fail suddenly or swell, which no capacity figure predicts.

Take this with you

How this calculation works

Every rechargeable battery loses capacity with age. Health is simply the full-charge capacity now, divided by the capacity it had when new (design capacity). Read both figures from your device’s battery report and enter them; the tool does the division. Above 80% is healthy, below 50% is significantly worn.

What the results mean

Health: How much of the original capacity remains. 100% is new; batteries are considered healthy down to about 80%.
Wear: The share of original capacity lost. 20% wear means the battery holds four-fifths of what it did new.

Common problems and fixes

The health figure is over 100%: The capacities are swapped, or in different units. Design capacity is the larger, original figure; full-charge is what it holds now. Both must be mAh, or both Wh.
Where do I find these numbers?: On Windows, run "powercfg /batteryreport" and open the HTML file. On macOS, the System Information battery section lists them. On Linux, upower or the /sys/class/power_supply files have them.

Frequently asked questions

Why can’t a website just read my battery health?

Because browsers deliberately cannot. The old Battery Status API was removed for privacy reasons, and even when it existed it never exposed capacity or health — only charge level. Reading design and full-charge capacity requires a native tool with system access. This calculator takes those native figures and does the maths, which is all a web page can honestly do.

At what health should I replace the battery?

There is no hard rule, but below 80% you will notice shorter runtime, and below 50% it becomes limiting. The real question is whether the shorter runtime bothers you for how you use the device — the health figure tells you what you are working with.

Put this on your own site

Free to embed, no attribution required beyond the source link the frame carries itself. It runs entirely in your visitor's browser, sets no cookies and loads no third-party script.

Embed code

<iframe src="https://runthetests.com/embed/battery-health-calculator/" width="100%" height="560" style="border:1px solid #e5e5e5;border-radius:8px" title="Battery Health Estimator" loading="lazy"></iframe>

Preview it at https://runthetests.com/embed/battery-health-calculator/. Embedded pages are marked noindex, so yours stays the canonical copy — not this one.