Battery Life Calculator — calculate battery life for tech projects. Formula, specs, and practical notes.
Battery life (hours) = Capacity (mAh) ÷ Current draw (mA)
Adjusted: Life = Capacity ÷ (Current ÷ Efficiency%)
Convert Wh to mAh: mAh = Wh × 1,000 ÷ Voltage (V)
Worked examples: Smartphone — 4,000 mAh battery, 200 mA average draw, 85% efficiency. Life = 4,000 ÷ (200 ÷ 0.85) = 17 hours. IoT sensor — 1,000 mAh, 2 mA average draw. Life = 1,000 ÷ 2 = 500 hours ≈ 20 days. Laptop — 60 Wh at 14.4V = 4,167 mAh, 1,500 mA draw. Life = 4,167 ÷ 1,500 = 2.8 hours.