Free online battery life calculator. Estimate how long your device battery will last based on capacity, voltage, and power consumption. Supports phones, laptops, tablets, and custom devices.
Battery Life Calculator helps you estimate how long your device will run on a single charge. Enter your battery capacity (mAh), voltage (V), and device power consumption (W) or current draw (mA) to get an accurate runtime estimate. Useful for comparing devices, planning power usage, or estimating backup power needs.
Battery life is calculated using the formula: Battery Life (hours) = (Capacity in mAh × Voltage in V) / (Power Consumption in W × 1000). For example, a 5000mAh battery at 3.7V with a 5W device gives: (5000 × 3.7) / (5 × 1000) = 3.7 hours.
mAh (milliampere-hour) is a unit of electric charge that measures battery capacity. It tells you how much current a battery can deliver over time. A 5000mAh battery can deliver 5000mA for one hour, or 2500mA for two hours. Higher mAh means longer battery life, but only when comparing batteries with the same voltage.
Battery capacity (mAh) and voltage (V) are usually printed on the battery itself, or listed in your device settings (About Phone/Device → Battery Information). You can also find them on the manufacturer website or product specifications page.
Real-world battery life varies due to screen brightness, background apps, temperature, battery age/health, network activity (WiFi, 5G), and usage patterns. Our calculator gives a theoretical maximum; actual usage is typically 70-90% of the estimate.
Yes, completely free. No ads, no registration, no limits. All calculations happen locally in your browser — your data never leaves your device.