How to Use Battery Charge Time Calculator
The Battery Charge Time Calculator estimates how long it takes to charge a phone, laptop, power bank, EV battery or AA/AAA cell from current percentage to a target percentage. Enter the battery capacity, current and target levels, and the charger output; the Battery Charge Time Calculator outputs hours and minutes.
- Enter battery capacity — mAh, Ah or Wh.
- Enter battery voltage — required for mAh and Ah inputs.
- Set current and target percentage — e.g. 20% to 100%.
- Enter charger output — V × A or directly W.
- Set efficiency — typically 85-90%.
Formula & Theory — Battery Charge Time Calculator
The Battery Charge Time Calculator is energy-based:
Energy (Wh) = Capacity (mAh) × Voltage / 1000
= Capacity (Ah) × Voltage
Needed Energy = Energy × (Target % - Current %) / 100
Effective Power = Charger Power × Efficiency
Charge Time (h) = Needed Energy / Effective Power| Symbol | Meaning |
|---|---|
| Capacity | mAh, Ah or Wh rating on the battery |
| Voltage | Nominal battery voltage |
| Efficiency | Fraction of input energy stored |
Assumptions and Limits
The Battery Charge Time Calculator assumes constant power. In practice, charging is faster between 20% and 80% and slows above 90% due to constant-voltage trickle charging.
Use Cases for Battery Charge Time Calculator
- Smartphones — estimate fast-charge time with 18W, 25W, 65W chargers.
- Laptops — see if a USB-C 65W charger can fully replenish overnight.
- Power banks — plan charging during travel.
- AA/AAA NiMH cells — match charger current to capacity.
- EV batteries — estimate level 1/2 home charging hours.