What CheckBatteryHealth measures
CheckBatteryHealth uses reported battery capacity values to estimate how much of the battery's original designed energy capacity remains available at full charge.
The two values used by the core calculation are Design Capacityand Full Charge Capacity. On supported Windows battery reports, these values are reported in milliwatt-hours (mWh).
The resulting percentage is a capacity-retention estimate. It is not a universal measurement of battery safety, physical condition, instantaneous runtime, or every component of battery performance.
Design Capacity
Design Capacity is the battery capacity reported as the intended or designed energy capacity of the battery.
In Windows battery information, Microsoft documents DesignCapacityInMilliwattHoursas the estimated energy capacity of a new battery of that type.
Example
A battery with a reported Design Capacity of 60,000 mWhhas a reference capacity of 60,000 mWh for the calculation.
Full Charge Capacity
Full Charge Capacityrepresents the reported amount of energy the battery can currently hold when fully charged.
Microsoft documents this value as FullChargeCapacityInMilliwattHoursin its Windows battery reporting APIs.
Because a battery can lose capacity as it ages, this value can become lower than the original Design Capacity.
Design Capacity
60,000 mWh
Reference capacity
Full Charge Capacity
48,000 mWh
Currently reported capacity
The calculation
The core battery-health calculation compares Full Charge Capacity with Design Capacity.
Battery health estimate
(Full Charge Capacity ÷ Design Capacity) × 100
Worked example
Design Capacity = 60,000 mWh
Full Charge Capacity = 48,000 mWh
48,000 ÷ 60,000 × 100 = 80%
In this example, the reported full-charge capacity is 80% of the reported design capacity.
Unit compatibility
The two capacity values must represent comparable quantities before the percentage is calculated.
Windows battery reports commonly express the relevant energy capacity values in mWh. If values are supplied manually, the units must be compatible with each other.
Comparable values
Both values describe the same type of energy capacity.
Don't mix unlike values
A calculation should not combine incompatible measurements.
Windows Battery Report
Windows provides battery-reporting tools that can expose information about battery usage and capacity. Microsoft documentspowercfg /batteryreportas a command for generating a battery usage report.
powercfg /batteryreportOn supported reports, the relevant capacity information can be used to obtain Design Capacity and Full Charge Capacity values.
CheckBatteryHealth uses these reported values for the capacity calculation. It does not attempt to turn every field in a Windows battery report into a single diagnostic score.
Important
Microsoft notes that battery report properties can be unavailable when the battery controller does not report a value. A missing value therefore should not be silently invented or substituted.
Manual calculation
You can calculate the same capacity percentage manually if you already have compatible Design Capacity and Full Charge Capacity values.
- 1Find the reported Design Capacity.
- 2Find the reported Full Charge Capacity.
- 3Confirm that both values use compatible units.
- 4Divide Full Charge Capacity by Design Capacity.
- 5Multiply the result by 100.
The analyzer is intended to make this process easier by presenting the relevant values and calculation without requiring users to perform the arithmetic themselves.
How report processing works
When a supported Windows battery report is uploaded for analysis, the service processes the report to locate the battery information needed for the calculation.
Upload
Provide a supported battery report.
Parse
Read the relevant battery fields.
Calculate
Compare the reported capacities.
Explain
Return the result with context and limitations.
The system does not need to invent a capacity value when a report contains no usable capacity data. Unsupported or incomplete input may therefore result in an error or unavailable result rather than a fabricated percentage.
What the result can tell you
The calculated percentage is most useful as an indication of reported capacity retention relative to the battery's reported design capacity.
How the reported full-charge capacity compares with the reported design capacity.
Whether the reported capacity has declined substantially from the design reference.
A useful starting point for investigating reduced runtime or battery wear.
A consistent number that can be tracked over time when the underlying reporting data is comparable.
What it cannot tell you
A capacity percentage should not be interpreted as a complete physical battery diagnosis.
It does not determine whether a battery is physically swollen.
It does not identify every electrical or charging fault.
It does not predict exact remaining runtime.
It does not replace manufacturer diagnostics or professional inspection.
It does not determine whether a battery is safe to continue using.
It does not explain every cause of sudden shutdowns or unexpected percentage changes.
If a battery is physically damaged, swollen, unusually hot, leaking, smoking, or otherwise showing a safety concern, stop relying on a percentage calculation and follow appropriate manufacturer or professional safety guidance.
Why results can exceed 100%
The calculation compares two reported values. It does not impose an artificial 100% ceiling.
If the reported Full Charge Capacity is greater than the reported Design Capacity, the mathematical result can therefore exceed 100%.
Design
50,000 mWh
Full charge
51,500 mWh
Result
103%
CheckBatteryHealth preserves the mathematical result rather than silently changing it to 100%. An above-100% result should be treated as a property of the reported values, not as proof that a battery has gained physical capacity beyond every possible reference.
Accuracy and limitations
The arithmetic itself is deterministic: given two valid capacity values, the formula produces the corresponding ratio. The important limitation is the quality and meaning of the values being reported.
What can affect interpretation?
- The operating system and battery controller must provide usable capacity information.
- Different devices may expose battery information differently.
- A capacity estimate does not capture every aspect of battery condition.
- Reported values can change over time and should be interpreted in context.
For that reason, CheckBatteryHealth presents the calculation as an estimate based on reported capacity rather than claiming laboratory measurement or complete diagnostic accuracy.
Data processing
CheckBatteryHealth has two distinct calculation paths: manual values and supported Windows battery reports.
Manual calculation
Values entered by the visitor
The supplied capacity values are used to perform the calculation according to the methodology described above.
Windows report
Report submitted for analysis
A supported battery report is processed to extract the relevant capacity information needed for the calculation.
For the current details of data collection, processing, retention, and related privacy practices, see the Privacy Policy.
Privacy
Privacy is part of the methodology because the way battery information is handled affects how the analyzer should be understood.
Manual calculations and uploaded Windows reports are not presented as the same processing flow. The privacy documentation explains what information is processed and why.
Transparency over marketing claims
CheckBatteryHealth does not describe uploaded Windows reports as local-only processing when the report is sent to the analysis service.
Read the full CheckBatteryHealth Privacy Policy for the current details.
Sources
The methodology is designed around the battery information exposed by supported operating-system and device reporting systems. The following primary sources provide relevant technical documentation.
Microsoft Learn — Get battery information
Documents battery reports and capacity properties including Design Capacity and Full Charge Capacity.
Microsoft Learn — Powercfg command-line options
Documents the powercfg /batteryreport command and its report-generation options.
Microsoft Learn — BatteryReport class
Documents battery report properties and the meaning of reported capacity values.
Apple Support — Determine battery cycle count for Mac laptops
Provides Apple's guidance on battery cycles and capacity-related battery information.
Apple Support — Battery health management
Explains battery ageing, capacity changes, and battery-health management on supported Mac laptops.
Manufacturer documentation can change over time. Device behavior can also vary by model, operating system, battery controller, and firmware.
Methodology owner
A. Ali
Founder & Developer, CheckBatteryHealth
The methodology is intended to make the calculation transparent and to clearly distinguish reported battery capacity from broader battery diagnostics.