Battery Charge Time Calculator
Plug in battery specs and charger output to estimate how long it takes to reach your desired charge level.
Typical USB chargers are 80–90% efficient.
Energy needed: 4,250 mAh
Ideal charge time (100% efficient): 2 hours 8 minutes
Actual charge time (with losses): 2 hours 30 minutes
Total minutes: 150 minute(s)
How to Use This Calculator
Enter battery and charger specs
Use the battery capacity (mAh) and charger current from device manuals or product labels.
Set start and target percentages
Estimate your current charge and choose the percentage you want to reach.
Adjust efficiency
Lower efficiency if you use wireless charging or older cables; increase for modern USB-C PD chargers.
Formula
Required mAh = Capacity × (Target% − Start%) ÷ 100
Ideal Hours = Required mAh ÷ Charger mA
Actual Hours = Ideal Hours ÷ (Efficiency ÷ 100)
Example: 5000 mAh battery, 2 A charger, 15%→100%, 85% efficiency → Required 4250 mAh → 2.5 hours ideal → 2.94 hours actual.
Planning Charge Sessions
- Combine with a power bank’s capacity to estimate how many top-ups you get on a trip.
- Lower the target percentage (e.g., 80%) to extend battery longevity.
- Account for fast-charging phases—many devices charge quickly to 50% then taper.
- Use higher efficiency for wired, high-quality USB-C cables and PD adapters.
Frequently Asked Questions
Why is real charging slower near 100%?
Charging controllers taper current to protect the battery. The calculator assumes average power—expect longer times in the final 10%.
Does wireless charging change efficiency?
Yes—wireless pads are often 60–75% efficient. Reduce the efficiency slider to match the charger you use.
Can I use this for power banks?
Absolutely. Treat the battery capacity as the power bank’s capacity and include its USB output current.
What if I only know watts?
Convert to amps: charger current (A) = power (W) ÷ voltage (V). Multiply by 1000 for mA.