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CheckBatteryHealth methodologyAnalyzer documentation

How CheckBatteryHealth Calculates Battery Health

A transparent look at the battery data, calculation, validation rules, analyzer tests, limitations, and privacy behind the reported battery-health percentage.

Analyze your batteryRead the Windows report guide
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What this page documents

This page documents the calculation and behavior of the analyzer rather than repeating general battery advice. The goal is reproducibility: users can see the source values, arithmetic, validation rules, test cases, and limits of the result.

01 · Product purpose

Why we built CheckBatteryHealth

Battery reports can contain useful capacity data without turning those numbers into an immediately understandable percentage. CheckBatteryHealth was built to make that relationship easier to calculate and interpret.

The analyzer is deliberately focused on a specific question: how does the battery's currently reported Full Charge Capacity compare with its Design Capacity?

That makes the result useful as a starting point for investigation, while keeping the raw capacity values and other diagnostics in view.

02 · Source data

What the battery report provides

On supported Windows systems, a battery report can expose fields such as Design Capacity and Full Charge Capacity. Those values come from the battery, its controller, firmware, drivers, and the operating system's reporting layer.

CheckBatteryHealth does not create those underlying measurements. It uses the reported values supplied by the device or report and applies the documented calculation and validation rules.

Primary terminology

For Windows battery terminology, see Microsoft's Design Capacity documentationMicrosoft Learn.

03 · Core calculation

The battery-health calculation

When Design Capacity and Full Charge Capacity are available, belong to the same battery, and use compatible units, the reported capacity-health percentage is based on their ratio.

The formula

Full Charge Capacity ÷ Design Capacity × 100

Example

Design Capacity: 50,000 mWh
Full Charge Capacity: 45,000 mWh
45,000 ÷ 50,000 × 100 = 90%

04 · Worked examples

Simple results you can reproduce

100% — no reported capacity difference

50,000 ÷ 50,000 × 100 = 100%.

84% — reduced reported capacity

42,000 ÷ 50,000 × 100 = 84%.

56% — substantially reduced reported capacity

28,000 ÷ 50,000 × 100 = 56%.

103% — reported capacity above the reference

51,500 ÷ 50,000 × 100 = 103%.

05 · Data validation

Validation happens before the math

A mathematically correct formula can still produce a meaningless result if the inputs are wrong. The analyzer therefore needs usable, comparable capacity values before treating the calculation as valid.

Same battery

Use the two capacity values from the same battery context.

Compatible units

Do not divide an mWh value directly by an mAh value and call the result a valid percentage.

Required values present

Missing or unavailable capacity values cannot produce a defensible percentage.

Valid denominator

A zero or unusable Design Capacity cannot be used as the calculation denominator.

06 · Software verification

Battery Analyzer Test Cases

These cases document the analyzer's expected calculation and validation behavior across normal, unusual, incomplete, and malformed inputs. The numerical cases are independently reproducible from the displayed inputs.

Battery Analyzer Test Cases
TestInputExpectedBehavior
Test ANormal capacityDesign Capacity50,000 mWhFull Charge Capacity45,000 mWh90%Calculate normally
Test BLow capacityDesign Capacity50,000 mWhFull Charge Capacity28,000 mWh56%Calculate normally
Test CAbove 100%Design Capacity50,000 mWhFull Charge Capacity51,500 mWh103%Keep the reported ratio
Test DDifferent unitsDesign Capacity50,000 mWhFull Charge Capacity4,500 mAhInvalid inputReject incompatible units
Test EMissing capacityDesign CapacityMissingFull Charge Capacity45,000 mWhInvalid reportDo not calculate
Test FMalformed HTMLInputMalformed / invalid HTMLParsing errorReturn an error state

What these tests demonstrate

  • • Normal capacity values produce the expected ratio.
  • • Lower capacity values produce proportionally lower results.
  • • Values above the design reference are not silently capped at 100%.
  • • Incompatible units are not treated as comparable capacity values.
  • • Missing required values do not become a fabricated percentage.
  • • Malformed report input is handled as an error rather than valid battery data.

07 · Windows workflow

How Windows battery reports fit into the analyzer

A common Windows workflow starts with the built-in powercfg /batteryreport command. Windows generates an HTML report containing battery information that can include the capacity fields needed for this calculation.

The report is the source of the battery values; the analyzer's role is to extract or accept the relevant data, validate it, calculate the ratio, and present the result in understandable terms.

Windows command

powercfg /batteryreport

Need the complete report explained?

Read the Windows Battery Report guide for report sections, capacity history, estimates, and troubleshooting.

08 · Scope and limitations

What the percentage cannot diagnose

Battery health is only one part of battery condition. A capacity percentage should not be presented as a complete hardware diagnosis.

Runtime

It cannot predict exactly how many hours a laptop will run.

Power consumption

CPU/GPU load, brightness, wireless activity, background software, and power settings affect runtime.

Charger faults

It cannot prove that a charger, cable, port, or charging circuit is working correctly.

Physical damage

It cannot inspect swelling, leakage, puncture damage, odor, or localized heat.

Cell-level faults

A percentage cannot inspect individual cells or prove that every cell is healthy.

Future failure

It cannot predict the exact date or moment a battery will fail.

09 · Data handling

Privacy and battery-data processing

Battery reports can contain device-specific information, so data handling is important when using an online analyzer. CheckBatteryHealth states that calculations are processed securely in the browser or through its API and that submitted data is not stored.

Users should still avoid submitting files containing unrelated personal information and should review the current privacy policy before uploading a report.

Processing

The site states that calculations are processed securely in the browser or through its API.

Storage

The site states that submitted battery data is not stored.

10 · Methodology summary

The process in six steps

  1. 1

    Obtain the battery data

    Use the battery or report values supplied by the device.

  2. 2

    Match the capacity values

    Use Design Capacity and Full Charge Capacity from the same battery and compatible units.

  3. 3

    Validate the inputs

    Reject missing, unusable, incompatible, or malformed input.

  4. 4

    Calculate the ratio

    Full Charge Capacity ÷ Design Capacity × 100.

  5. 5

    Present the result

    Show the reported capacity relationship without implying a complete diagnosis.

  6. 6

    Keep limitations visible

    Explain what the percentage cannot determine, including runtime and physical safety.

Methodology reviewed

September 15, 2026

Update this page when the product's calculation, validation behavior, privacy behavior, or supported report-processing workflow materially changes.

11 · Questions and answers

Frequently asked questions

How does CheckBatteryHealth calculate battery health?

When usable values are available, CheckBatteryHealth compares Full Charge Capacity with Design Capacity using (Full Charge Capacity ÷ Design Capacity) × 100.

What battery data does the calculation use?

The core calculation uses Design Capacity and Full Charge Capacity from the same battery and compatible capacity units.

Can battery health be above 100%?

Yes. A reported Full Charge Capacity can be higher than the reported Design Capacity, producing a result above 100%. That is a ratio of reported values, not proof that the physical cells gained capacity.

What happens if battery capacity data is missing?

A valid percentage should not be produced when the required capacity values are missing, unusable, or cannot be compared reliably.

Can the battery-health percentage predict runtime?

No. Runtime also depends on workload, display brightness, wireless activity, power settings, temperature, background processes, and other system conditions.

Can CheckBatteryHealth determine whether a battery is physically safe?

No. A capacity calculation cannot inspect swelling, leakage, puncture damage, unusual odor, localized heat, or individual cell faults.

Does CheckBatteryHealth store my battery report?

The site states that battery calculations are processed securely in the browser or through its API and that submitted data is not stored. Review the current Privacy Policy for the latest details.

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