Battery capacity measures how much energy a battery can store, typically expressed in mAh (milliamp-hours) or Wh (watt-hours). mAh indicates how long a battery can supply a given current, while Wh represents total stored energy. Understanding battery capacity is essential for choosing the right battery and estimating device runtime.
1. Select calculation mode: Capacity Conversion, Runtime Estimation, or Charge/Discharge
2. Enter battery parameters: capacity, voltage, current draw, or charge current
3. View real-time results — all conversions and calculations happen automatically
Phone/Tablet Users: Estimate device runtime and understand battery health. A 4000mAh battery with 500mA draw lasts about 6.8 hours.
DIY Electronics: Choose the right battery for your project. An Arduino project using a 2000mAh Li-Po at 200mA draw runs about 8.5 hours.
EV Owners: Understand battery capacity vs range. A 48V 20Ah battery stores 960Wh, providing about 3.8 hours at 250W draw.
Lithium battery nominal voltage is typically 3.7V (single cell), but actual voltage ranges from 3.0V to 4.2V. mAh to Wh conversion requires voltage: 1mAh at 3.7V equals 0.0037Wh, at 5V equals 0.005Wh. Charge rate (C) indicates charging speed: 1C means full charge in 1 hour, 0.5C means 2 hours. Fast charging typically uses 0.5C-1C rates.
mAh (milliamp-hours) measures how long a battery can supply current. Wh (watt-hours) measures total stored energy. The relationship: Wh = mAh × Voltage(V) / 1000. A 3000mAh battery at 3.7V (11.1Wh) stores more energy than at 1.5V (4.5Wh).
Battery runtime = Battery capacity(mAh) / Device current draw(mA). Example: 3000mAh battery with 500mA draw = 6 hours. Actual runtime is typically 80-90% of theoretical value.
Charging time = Battery capacity(mAh) / Charging current(mA) × Efficiency factor (1.2-1.5 for lithium). Example: 3000mAh at 1000mA = 3.6 hours with 1.2 efficiency.
Common nominal voltages: Single cell Li-ion/Li-Po 3.7V (full 4.2V, cutoff 3.0V); LiFePO4 3.2V; NMC 3.6V-3.7V. Multi-cell series doubles voltage per cell.
Yes. Lithium batteries typically retain 80% capacity after 500 cycles. High temperatures, overcharging, and deep discharging accelerate degradation.
Professional: Use a battery analyzer for constant-current discharge to cutoff voltage. Simple: Charge fully, use until shutdown, compare with rated capacity. Replace below 80%.