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Repair Windows errors before they cause bigger problemsFix Now →Scan for outdated or missing drivers - takes under a minuteDriver Scan →Check your phone’s built-in battery health or diagnostic screen first, but know what it reports: a health percentage usually estimates capacity relative to when the battery was new, not the battery’s current capacity in mAh. To calculate watt-hours (Wh), you also need the battery’s nominal voltage: Wh = (mAh ÷ 1,000) × volts.
Check what your phone reports
Menu names and available readings depend on the phone model and software. A battery-health estimate, a diagnostic result, and the original capacity rating answer different questions; none should automatically be treated as a direct measurement of the installed battery’s remaining mAh.
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iPhone
- iPhone 15 and later with iOS 17.4 or later: Open Settings → Battery → Battery Health. Apple says this screen can show maximum capacity, cycle count, manufacture date, first-use date, and a replacement recommendation. See Apple’s iPhone battery and performance guidance.
- iPhone 11, 12, 13, and 14: Open Settings → Battery → Battery Health & Charging. Menu details can vary by model and software version.
Apple defines maximum capacity as the device battery’s capacity relative to when it was new; it is not necessarily an absolute mAh reading. Apple’s broader guidance says iPhone 6 and later include Battery Health features. If a supported newer iPhone says it cannot verify the battery, its battery details may not be accurate; seek a manufacturer service assessment rather than relying on the displayed health figure. See Apple’s battery and performance information.
Google Pixel
On Pixel 8a and later, open Settings → Battery → Battery health → Battery capacity to see the estimated capacity. Google says battery health status is available only on Pixel 8a and later; Pixel 6a, Pixel 7, Pixel 7 Pro, Pixel 7a, Pixel 8, and Pixel 8 Pro do not indicate battery health status. Google describes the estimate as remaining capacity compared with original capacity and cautions that initial values are based on lab results and may differ from the actual battery state. See Google’s Pixel battery guidance.
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Samsung Galaxy
Open Samsung Members → Support → Phone diagnostics, then check or test battery status. Labels and availability can vary by app and device version. Samsung documents a battery-status diagnostic, not a universal readout of remaining mAh or Wh. For frequent unexpected shutdowns or a noticeable decline in battery life, Samsung recommends evaluation at a service center. See Samsung’s Galaxy battery information.
Other Android phones
Look in the manufacturer’s battery settings or diagnostic app, and consult support instructions for your exact model. There is no single Android menu path or universal health screen. If the phone does not provide an estimate, its original specification or battery label may state nominal mAh and voltage, but those figures do not tell you the battery’s present condition.
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Convert mAh to watt-hours
mAh measures electric charge capacity. Wh measures energy and incorporates voltage, so mAh alone is not enough to calculate Wh. Convert mAh to amp-hours by dividing by 1,000, then multiply by nominal battery voltage:
Wh = (mAh ÷ 1,000) × nominal voltage (V)
For example, a hypothetical 5,000 mAh battery at a nominal 3.85 V works out to 19.25 Wh. These are assumed values for explaining the calculation, not a specification for a particular phone.
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- Multi-Device Compatibility & Safety Features: This battery capacity tester supports discharge aging tests for a wide range of devices, including chargers, cables, power banks, batteries, and power adapters. It has intelligent safety protection such as overload, overcurrent and high temperature protection, real-time monitoring of status makes it safe and reliable.
- Four Discharge Modes & App Compatibility: The USB load tester supports constant current, constant power, constant resistance, and constant voltage modes. It is compatible with Android and iOS apps, as well as PC BT and wired connections, providing versatile testing options.
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As a separate published illustration, iFixit gives the calculation 5,200 mAh × 10.8 V ÷ 1,000 = 56.16 Wh for a FixHub battery pack; those are not phone-battery specifications. See iFixit’s explanation of mAh and battery capacity.
When comparing batteries at different voltages, Wh is the clearer energy comparison. A larger mAh number alone does not guarantee more energy.
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- Multi-function: This USB tester is designed to detect voltage, current, capacity, electric quantity, power, temperature, resistance, charging time and other data of the USB C devices, which is convenient for testing power supply and quality.
- Detect Various Fast Charging Protocols: The Type-C USB tester supports QC2.0/3.0/4.0 and Super VOOC protocol charging, but the name of the fast charging protocol will not be displayed on the USB tester.
- Measuring Data is Guaranteed: Power-off storage function that stores capacity and energy data when the mobile power is turned off, which is convenient for subsequent viewing and convenient for capacity energy measurement of mobile power.
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- Button Function: 1.Click the button once to switch screens in a cyclical manner; 2.Double-click the button to rotate the displayed content; 3.Press and hold the button (3 seconds): Clear all capacity, amount of electricity, and time.
Know what a capacity rating means
A published capacity is generally a rating for a new battery, not a live measurement of an older phone’s remaining capacity. Manufacturers may also distinguish between a typical value and a minimum rated value. Huawei, for example, defines typical capacity as an average actual capacity for a production batch and rated capacity as the minimum under IEC 61960 test conditions. Preserve that distinction when comparing specifications. See Huawei’s explanation of typical and rated capacity.
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Cycle-life statements are also conditional design guidance, not a guarantee for every device. Apple says iPhone 14 models and earlier are designed to retain 80% of original capacity after 500 complete charge cycles under ideal conditions, and iPhone 15 models after 1,000 such cycles. Apple notes actual capacity depends on how a phone is regularly used and charged. Google says Pixel 3 through Pixel 8 Pro and Pixel Fold can retain up to 80% capacity for about 800 charge cycles, while Pixel 8a and later can do so for about 1,000 cycles. On supported Pixel models, Google labels remaining capacity below 80% as “Reduced”; that is Google’s device-specific status threshold, not a universal replacement rule. See Apple’s battery guidance and Google’s Pixel battery guidance.
Quick Recap
How to use the result
- If the screen gives a health percentage, treat it as a relative estimate unless the manufacturer explicitly identifies it as an absolute capacity reading.
- If you need Wh, find the nominal voltage for the same battery and use the formula above; do not infer voltage from mAh.
- If a diagnostic reports reduced health, the phone recommends replacement, or the battery is causing unexpected shutdowns, follow the manufacturer’s model- and region-specific service options.
- A USB charging meter measures the charging connection, not the installed battery’s remaining mAh or Wh. An app or meter should not be treated as a universal direct capacity test.
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