Device Battery Runtime Calculator

Battery Runtime tells you how long a device will operate on a single charge based on the battery capacity and device power consumption.

The basic formula: Runtime (hours) = Battery Capacity (mAh) / Device Current Draw (mA)

Or using watt-hours: Runtime (hours) = Battery Energy (Wh) / Device Power (W)

Converting between units: Watt-hours (Wh) = milliamp-hours (mAh) × Voltage / 1000 mAh = Wh × 1000 / Voltage

Common battery capacities:

• Smartphone: 3,000-5,000 mAh (3.7V = 11-18.5 Wh)
• Tablet: 5,000-10,000 mAh (3.7V = 18.5-37 Wh)
• Laptop: 40-100 Wh (10,800-27,000 mAh at 3.7V)
• Power bank: 5,000-26,800 mAh
• AA battery: 2,500 mAh (1.5V = 3.75 Wh)
• 18650 Li-ion cell: 2,500-3,500 mAh (3.7V = 9.25-12.95 Wh)

Common device power consumption:

• LED flashlight (low): 0.1W
• LED flashlight (high): 3-10W
• Bluetooth speaker: 2-5W
• Smartphone (active use): 2-4W
• Smartphone (standby): 0.1-0.3W
• Tablet: 3-8W
• Laptop (light use): 10-25W
• Laptop (heavy use): 30-65W

Efficiency factor: Real-world runtime is typically 70-85% of the theoretical calculation due to:

• Voltage conversion losses (5-15%)
• Battery chemistry not delivering full capacity under load
• Temperature effects on battery performance
• Battery degradation over charge cycles

Battery aging: Lithium-ion batteries typically retain 80% of their original capacity after 300-500 full charge cycles. After 500 cycles, a 5,000 mAh battery effectively becomes a 4,000 mAh battery.

The 80% rule: For practical estimates, multiply your theoretical runtime by 0.8 to get a realistic estimate.