Battery Capacity Converter

Battery capacity measures how much electrical energy a battery can store and deliver over time. It is expressed in several units depending on the context: milliamp-hours (mAh) for small batteries like phones, amp-hours (Ah) for automotive and deep-cycle batteries, watt-hours (Wh) for true energy comparison, kilowatt-hours (kWh) for grid-scale storage, and joules (J) for scientific applications. Understanding these units and how they relate is essential for comparing batteries across different voltage levels.

The most common unit, milliamp-hours (mAh), describes how many milliamps a battery can supply for one hour. However, mAh alone does not tell the full story because it does not account for voltage. A 1,000 mAh battery at 3.7 volts stores twice as much energy as a 1,000 mAh battery at 1.8 volts. For accurate comparison, watt-hours (Wh) — calculated as mAh × voltage ÷ 1,000 — is the preferred metric.

This converter translates between mAh, Ah, Wh, kWh, and joules, and provides practical runtime estimates for common devices like smartphones, tablets, and laptops. It also calculates battery equivalents, showing how many AA batteries, 18650 cells, or other standard batteries your capacity represents.

Converting between battery capacity units requires understanding the relationship between charge (amp-hours) and energy (watt-hours), which involves the battery voltage.

The converter provides several useful outputs beyond simple unit conversion:

• Runtime estimates: Calculated by dividing the Wh capacity by the typical power consumption of various devices. A smartphone averages about 3W, a tablet about 5W, and a laptop about 30W.
• Battery equivalents: Shows how many common batteries (AA, AAA, 18650, CR123A, etc.) your capacity represents, making it easy to visualize the energy content.
• Energy cost: Calculates the electricity cost to charge the battery at $0.12/kWh, the US average residential rate.
• C-rate reference: The 1C rate equals the Ah capacity — a 2,000 mAh battery delivers 2A at 1C. This helps understand charge and discharge speed limits.

The battery capacity converter accepts three inputs for flexible calculations:

1. Enter the capacity value: Type the numerical capacity of your battery in the selected unit.
2. Select the unit: Choose from mAh, Ah, Wh, kWh, or joules depending on how your battery is rated.
3. Enter the voltage: Specify the nominal voltage of the battery. Quick-select buttons for common voltages (3.7V Li-ion, 5V USB, 12V car battery, etc.) are provided below the input.

The results section displays the equivalent capacity in all five units, device runtime estimates, battery equivalents, and energy cost information.

Battery capacity knowledge is critical for mobile device users comparing power banks, replacement batteries, and portable chargers. A "20,000 mAh" power bank at 3.7V stores 74 Wh of energy — enough to charge a typical smartphone approximately 4-5 times. Understanding the voltage is key: the same 20,000 mAh at 5V USB output is only equivalent to 14,800 mAh due to conversion losses.

Electric vehicles and renewable energy storage use kWh to express battery capacity. A Tesla Model 3 Long Range has a 75 kWh battery pack, while a home battery system like the Tesla Powerwall stores 13.5 kWh. These numbers directly determine the vehicle's range or the home's backup duration.

In consumer electronics shopping, comparing batteries across brands and devices requires understanding capacity units. A laptop battery rated at 56 Wh and a phone battery at 15 Wh store vastly different amounts of energy, even though both might have similar mAh ratings when measured at different voltages.