Battery Capacity Explained: mAh vs Wh - Complete Guide

Reviewed: November 2025

Introduction: Understanding mAh vs Wh

Battery capacity ratings appear everywhere—smartphones advertise "4000 mAh batteries," laptops boast "60 Wh capacity," and powerbanks confuse consumers with both measurements. Understanding the difference between milliamp-hours (mAh) and watt-hours (Wh) is essential for making informed purchasing decisions, accurately comparing batteries across devices, and calculating how long your devices will run between charges. mAh measures electrical charge capacity—the quantity of electrical charge a battery can store. Wh measures energy capacity—the actual work the battery can perform. These aren't interchangeable: a 3000 mAh battery at different voltages stores vastly different amounts of energy. This comprehensive guide clarifies the distinction between mAh and Wh, explains conversion formulas, provides real-world examples from smartphones to electric vehicles, and offers practical tips for maximizing battery life and choosing the right devices.

What is mAh (Milliamp-Hours)?

Milliamp-hours (mAh) measure electrical charge capacity—specifically, the amount of electric current a battery can deliver over one hour. One milliamp-hour equals one milliampere (mA) of current flowing for one hour. A 3000 mAh battery can theoretically deliver 3000 milliamperes (3 amperes) for one hour, 1500 mA for two hours, or 300 mA for ten hours before depleting. This measurement quantifies the battery's charge storage—the total quantity of electrons it can move through a circuit.

Smartphone manufacturers predominantly use mAh ratings because most phone batteries operate at similar voltages (3.7-3.85V for lithium-ion cells). This makes mAh a convenient comparison metric within the smartphone category—a 4500 mAh phone generally outlasts a 3500 mAh phone if other factors (screen size, processor efficiency, software optimization) are equal. However, mAh alone doesn't tell the complete energy story because it ignores voltage, a critical component of electrical power.

The limitation of mAh becomes apparent when comparing batteries across different device categories or voltage classes. A laptop battery rated at 4000 mAh and 11.1V stores far more energy than a smartphone battery rated at 4000 mAh and 3.7V. The charge quantity (mAh) is identical, but the energy capacity differs by a factor of three. This is why professionals and regulatory bodies prefer Wh for accurate battery comparisons—it accounts for both charge and voltage.

What is Wh (Watt-Hours)?

Watt-hours (Wh) measure energy capacity—the actual work a battery can perform. One watt-hour equals one watt of power sustained for one hour. Unlike mAh, Wh accounts for both current (charge flow rate) and voltage (electrical pressure), providing a complete picture of stored energy. Energy (Wh) = Power (W) × Time (h), and power equals voltage multiplied by current (W = V × A), so Wh inherently incorporates voltage into the measurement.

Aviation regulations, international shipping standards, and professional electronics all use Wh as the standard battery capacity metric. Airlines limit powerbanks to 100 Wh (approximately 27,000 mAh at 3.7V) for carry-on luggage because Wh accurately represents fire risk regardless of voltage configuration. Laptop manufacturers specify batteries in Wh (typically 40-100 Wh) because laptop batteries use various voltage configurations (7.4V, 11.1V, 14.8V) making mAh comparisons meaningless without voltage context.

Understanding Wh empowers better purchasing decisions and device comparisons. A 50 Wh laptop battery stores the same energy regardless of voltage—whether it's a 6-cell 11.1V battery (4505 mAh) or a 4-cell 14.8V battery (3378 mAh). The Wh rating lets you directly compare energy capacity across devices, calculate runtime based on power consumption, and understand why your tablet outlasts your gaming laptop despite similar physical battery sizes. Learn more about energy measurements in our power vs energy guide.

Converting Between mAh and Wh

Converting mAh to Wh requires knowing the battery's voltage. The formula is: Wh = (mAh × Voltage) / 1000. The division by 1000 converts milliamp-hours to amp-hours, matching the watt-hour unit (since watts = volts × amps). For example, a smartphone battery rated at 4000 mAh and 3.7V nominal voltage contains (4000 × 3.7) / 1000 = 14.8 Wh of energy. Always use the nominal voltage (the average operating voltage) rather than maximum charging voltage for accurate calculations.

Converting Wh to mAh requires rearranging the formula: mAh = (Wh × 1000) / Voltage. A laptop battery rated at 56 Wh with 11.1V nominal voltage has (56 × 1000) / 11.1 = 5045 mAh capacity. This conversion is essential when comparing devices that list capacity in different units—you can normalize everything to Wh for accurate comparison regardless of voltage differences.

Common voltage standards simplify conversions: lithium-ion smartphone batteries typically use 3.7-3.8V nominal (4.2V max charge); laptop batteries commonly use 7.4V (2-cell), 11.1V (3-cell), or 14.8V (4-cell) configurations; USB powerbanks internally use 3.7V cells but output 5V. Always check the battery label or device specifications for exact voltage. Without voltage information, mAh cannot be converted to Wh—the measurement is incomplete. Use our energy converter for quick calculations across various energy units.

Real-World Examples: Smartphones, Powerbanks, and Laptops

Smartphones (3000-5000 mAh / 11-19 Wh): Modern smartphones typically feature 3000-5000 mAh batteries at 3.7-3.85V nominal voltage. Budget phones often include 3000-4000 mAh (11-15 Wh) batteries, mid-range devices sport 4000-4500 mAh (15-17 Wh), and flagship or gaming phones pack 4500-6000 mAh (17-23 Wh). The iPhone 14 Pro has approximately 3200 mAh (12.4 Wh), while Samsung Galaxy S23 Ultra features 5000 mAh (19.3 Wh). Despite lower mAh ratings, iPhones often achieve competitive battery life through superior software optimization and efficient processors.

Powerbanks (10,000-30,000 mAh / 37-111 Wh): Powerbank marketing often misleads consumers by advertising mAh at internal cell voltage (3.7V) while delivering power at USB output voltage (5V). A "10,000 mAh" powerbank contains 37 Wh of energy (10,000 × 3.7 / 1000) but delivers approximately 7,400 mAh at 5V accounting for conversion efficiency losses (typically 80-85%). Aviation regulations limit carry-on powerbanks to 100 Wh (roughly 27,000 mAh at 3.7V), and quantities above 160 Wh are prohibited entirely. Always check the Wh rating printed on quality powerbanks for honest capacity assessment.

Laptops (40-100 Wh): Laptop batteries use Wh exclusively because voltage configurations vary widely. Ultraportable laptops feature 40-60 Wh batteries for all-day productivity (8-12 hours light use). Standard laptops include 50-80 Wh batteries balancing performance and portability. Gaming laptops pack 80-100 Wh batteries to power high-performance GPUs, though runtime under gaming load often remains under 3 hours. The MacBook Air M2 has a 52.6 Wh battery achieving 15-18 hours through processor efficiency, while gaming laptops with 90 Wh batteries may only last 4-5 hours due to power-hungry components consuming 15-25W continuously.

Electric Vehicles and Large-Scale Batteries

Electric vehicles (EVs) use kilowatt-hours (kWh)—thousands of watt-hours—as the standard capacity metric because battery packs store enormous energy quantities at high voltages (300-800V systems). A Tesla Model 3 Long Range features a ~75 kWh (75,000 Wh) battery pack, equivalent to approximately 5,000 smartphone batteries or 1,500 laptop batteries. Expressing this in mAh would be meaningless without voltage context and would yield unwieldy numbers like 93,750,000 mAh at 800V.

EV range directly correlates with kWh capacity and efficiency (miles per kWh or kilometers per kWh). A 75 kWh battery achieving 4 miles/kWh efficiency provides 300 miles of range. Larger batteries offer longer range: compact EVs typically feature 40-60 kWh (150-250 mile range), mid-size EVs sport 60-80 kWh (250-350 miles), and luxury or long-range EVs pack 80-120 kWh (350-500+ miles). Charging infrastructure also references kWh—fast chargers deliver 50-350 kW of power, replenishing a 75 kWh battery in 20-60 minutes depending on charging curve and battery chemistry.

Home energy storage systems (like Tesla Powerwall) also use kWh ratings. A Powerwall stores 13.5 kWh of usable energy, sufficient to power essential home appliances during outages or optimize solar energy usage. Grid-scale battery installations feature megawatt-hours (MWh)—millions of watt-hours—storing enough energy to power thousands of homes. Understanding kWh helps compare energy costs across electricity bills, EV charging sessions, and renewable energy systems.

Why Wh is More Accurate Than mAh for Comparisons

Wh provides voltage-independent energy measurement, enabling accurate comparisons across different battery technologies, voltages, and device categories. A 50 Wh battery stores the same energy whether configured as 3.7V/13,514 mAh (single-cell smartphone), 11.1V/4,505 mAh (3-cell laptop), or 24V/2,083 mAh (power tool). The Wh rating directly represents energy capacity—the battery's ability to perform work—while mAh only measures charge without accounting for electrical pressure (voltage).

Regulatory bodies worldwide prefer Wh for safety classifications. International air transport regulations (IATA) limit lithium batteries based on Wh ratings: 100 Wh for passenger carry-on, 160 Wh for airline approval required. Fire risk correlates with total energy (Wh), not just charge quantity (mAh). A 27,000 mAh powerbank at 3.7V (100 Wh) poses similar risk to a 6,757 mAh laptop battery at 14.8V (100 Wh) despite vastly different mAh ratings. Safety testing, shipping classifications, and hazard assessments all reference Wh as the authoritative metric.

Professional electronics reviews and technical specifications increasingly emphasize Wh alongside mAh. Tech reviewers compare devices using Wh to provide fair assessments across product categories. When choosing between a 4500 mAh phone and a 4000 mAh phone, check the Wh ratings—if one uses a higher voltage battery configuration, the energy capacity difference may be negligible or even favor the lower mAh device. Always normalize to Wh when making informed purchasing decisions involving batteries from different manufacturers, voltage classes, or device types.

Practical Tips: How Long Will My Battery Last?

Calculating battery runtime requires knowing capacity (Wh or mAh) and power consumption (W or mA). For Wh batteries: Runtime (hours) = Battery Capacity (Wh) / Device Power Consumption (W). A laptop with a 60 Wh battery consuming 15W during web browsing lasts approximately 60 / 15 = 4 hours. Gaming at 45W reduces runtime to 60 / 45 = 1.3 hours. Power consumption varies dramatically with usage—screen brightness, processor load, wireless connectivity, and running applications all impact draw.

For mAh batteries: Runtime (hours) = Battery Capacity (mAh) / Current Draw (mA). A smartphone with 4000 mAh battery drawing 400 mA on average lasts approximately 10 hours. Light usage (reading, messaging) might draw 200 mA (20 hours runtime), while gaming could draw 1000 mA (4 hours). Modern smartphones display estimated runtime in settings based on recent usage patterns, providing more accurate predictions than simple capacity calculations.

Maximizing battery life involves reducing power consumption: lower screen brightness (often 20-30% of total power), disable unnecessary wireless features (Bluetooth, GPS when unused), close background apps, use dark mode on OLED screens (pixels off consume zero power), enable power-saving modes during critical low-battery situations. Battery health degrades over time—lithium-ion batteries typically retain 80% capacity after 300-500 full charge cycles (1-2 years typical use). Replace batteries when runtime becomes unacceptable, or consider upgrading to devices with larger capacities or more efficient components.

Quick Reference: Common Battery Capacities

Conclusion

Understanding battery capacity requires distinguishing between mAh (charge capacity) and Wh (energy capacity). While mAh provides convenient comparison within similar devices and voltage classes, Wh offers voltage-independent energy measurement essential for accurate comparisons across device categories, regulatory compliance, and runtime calculations. The conversion formula Wh = (mAh × Voltage) / 1000 bridges these measurements, enabling informed decisions when evaluating smartphones, laptops, powerbanks, and electric vehicles.

Whether you're purchasing a new smartphone, selecting a powerbank for travel, comparing laptop battery life, or understanding EV range specifications, prioritize Wh ratings for accurate energy capacity assessment. Combine this knowledge with device efficiency considerations, usage patterns, and charging infrastructure to make optimal choices. Battery technology continues advancing with higher energy densities, faster charging, and improved longevity—but the fundamental distinction between charge capacity (mAh) and energy capacity (Wh) remains constant across all battery chemistries and applications.