Phone Battery Health Calculator

How to Use This Tool

1. Find comparable full-charge and design capacity values in documented device information.
2. Enter both in the same unit and for the same battery. Do not use the current charge percentage.
3. Read the capacity ratio alongside the manufacturer's own reported status.

Full-Charge Capacity Is Different from Today’s Charge Level

Reported full-charge capacity describes the capacity the source says the battery can hold when fully charged. Design capacity is its reported reference capacity. Dividing the first by the second compares those quantities. A screen showing 40% charge describes the current level, not either raw capacity. Do not enter 40 as a full-charge capacity or multiply a reported capacity ratio by that charge percentage.

The calculation is exact arithmetic on supplied numbers; the source values may be estimates. Apple separates maximum capacity from peak-power performance. Google's Pixel guidance also describes estimated capacity and model-dependent reporting. A manual ratio cannot combine those assessments into a complete condition score. Its usefulness is checking a reported comparison while retaining the meaning and limits of the original source.

• Read the battery guide to choose compatible energy and power inputs

Find Two Values That Actually Belong Together

Keep the full-charge value, design reference, unit, battery identity, source and report date together. Both capacities must describe the same installed battery and a compatible reporting basis. After a battery replacement, use the replacement's documented values. A shop listing for another model, an aggregate for several batteries or a remembered original capacity can produce convincing arithmetic with an unsuitable denominator.

Some phones show a manufacturer percentage or status without both raw capacities. Read that information directly and consult the exact model's official guidance. Do not reconstruct two capacities from one percentage, substitute cycle count or assume an arbitrary app can expose them. This page neither reads device logs nor uploads reports. Missing source data remains missing rather than becoming the form's example values.

Make the Units Match Before Using the Selector

The single unit selector labels both inputs. Changing mAh to Wh does not transform the numbers. For example, entering 45000 from an mWh report beside 50 from a Wh reference gives 90000%, an arithmetic result from incompatible units. First convert confirmed 45000 mWh to 45 Wh, or convert 50 Wh to 50000 mWh. Then select the one shared unit.

Wh and mWh describe energy, with 1000 mWh equal to 1 Wh. mAh describes charge. Relating charge to energy requires an appropriate voltage and rating model; the selector does not perform that calculation. Even equal unit labels do not establish a compatible reference for different batteries. Preserve the source definitions instead of assuming that two similar-looking numbers must belong in the same comparison.

Read Ordinary, Above-Reference and Zero Results Carefully

The example 4500 ÷ 5000 × 100 gives 90%. Energy values 45 and 50 Wh give the same ratio, as do 45000 and 50000 mWh. These examples demonstrate unit cancellation for comparable inputs. They do not say the phone is currently charged to 90%, has exactly 90% of its original runtime or will lose a specified amount of capacity next month.

Values 5100 and 5000 give 102%, and the calculator preserves that result. Check battery identity, units, reference type and reporting quality before interpreting it. A supplied zero numerator gives 0%; an unavailable field, failed reading or unsupported-property sentinel is not a confirmed zero-capacity battery. There are no condition grades or replacement bands in this manual comparison.

Compare Dated Reports Rather Than Isolated Percentages

For a trend, retain the underlying capacities and the same source convention at each date. A changed design reference can move the percentage even when the full-charge estimate stays the same. A newly opened report may still contain an estimate that has not recently updated. Additional decimal places in this result do not improve the accuracy of the original report.

Apple documents reporting recalibration for specific iPhone 11 models, illustrating how an estimate can change after reporting updates. That is not a universal procedure or an instruction to force charge and discharge cycles. A higher later ratio alone cannot establish reversed wear. Compare source details and the manufacturer's messages before attributing a change to the battery itself.

Enter Clean Numbers and Keep the Result Within Its Scope

Enter ungrouped values such as 4500 and 5000, not numbers with thousands separators. Both values must be finite. Full-charge capacity can be zero or positive; design capacity must be positive. Negative entries, a zero denominator and overflowing results are rejected. Correct source units first rather than changing labels to make an implausible result look ordinary.

Use this comparison to check arithmetic and comparable observations. It does not establish a fault, remaining lifespan, warranty eligibility or a universal replacement decision. Runtime needs energy and average load; charge duration needs an interval and effective charging average. Follow the relevant manufacturer's reporting and diagnostic guidance for that device, rather than treating this one percentage as evidence for every battery question.

• Model operating time with available energy and average load
• Model the energy and time of a selected charging interval

What the Result Means

Readings vary with device reporting and estimation. Some phones expose only a percentage or status, not both raw capacities. Missing values cannot be inferred from today's charge level. The ratio does not establish faults, remaining lifespan or a replacement decision.

Common Questions