Device Battery Runtime Calculator
Calculate how long a battery will last in your device based on battery capacity and power consumption.
Compare battery sizes.
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.