Estimate how long it takes to charge a battery from any percentage. Supports phones, laptops, EVs, and power tools with efficiency accounting.
The Battery Charge Time Calculator estimates how long it takes to charge a battery from its current level to a target percentage. It works for phones, laptops, power banks, electric vehicles, and power tools, and it accounts for charging efficiency so the result is closer to real-world behavior than a simple division.
Charging is never perfectly efficient. Some energy is lost as heat in the charger, cable, and battery management system, and many devices slow down near the top of the charge range to protect battery health. That is why a 5,000 mAh phone does not behave like a clean linear math problem from 20% to 100%.
With device presets, adjustable current and target percentages, and a timeline-style estimate, this page answers the practical question of when a device will be usable again.
Charge-time estimates are easier to trust when they include battery capacity, charger power, and efficiency together. That matters when you are deciding whether a short plug-in window is enough or whether a longer charge is needed before you leave.
Wh Capacity = (mAh × Voltage) / 1,000 Energy Needed = Wh Capacity × (Target% - Current%) / 100 Actual Energy = Energy Needed / Efficiency Charge Time (hours) = Actual Energy / Charger Watts Charger Amps = Charger Watts / Voltage
Result: ~2h 21m (from 20% to 100%)
A 5,000 mAh phone battery at 5V has 25 Wh capacity. Charging 80% of that range (20% to 100%) needs 20 Wh delivered to the battery. At 85% efficiency, the charger must draw about 23.5 Wh from the wall. At 10W, that takes about 2.35 hours, with the final portion slowing down near the top of charge.
No charger is 100% efficient. Energy is lost as heat in the charger, cable, and battery management system. Wired USB-C chargers typically achieve 85-93% efficiency, while wireless Qi chargers drop to 60-75%. This lost energy increases your electricity bill and generates waste heat.
USB-PD can deliver up to 240W, Qualcomm Quick Charge up to 100W, and Tesla Superchargers up to 250kW. Faster charging generates more heat and may reduce long-term battery capacity. This calculator helps you compare charge times across different charger wattages.
Lithium-ion batteries last longest when kept between 20-80% charge. Charging to 100% or draining to 0% regularly degrades capacity over time. Many modern devices offer "optimized charging" that slows the last 20% to reduce wear.
Last updated:
Charging efficiency (typically 80-90%) means some energy is lost as heat. Also, most devices slow charging above 80% to protect battery health, which this calculator\'s efficiency factor partially accounts for.
mAh (milliamp-hours) measures charge capacity at a specific voltage. Wh (watt-hours) measures total energy. Wh = (mAh × Voltage) / 1000. Wh is more universal for comparing different-voltage batteries.
Check the charger\'s label for output watts, or multiply its output voltage by output amps. A 5V/2A charger is 10W. A 20V/3.25A laptop charger is 65W.
Lithium-ion batteries use constant-current/constant-voltage (CC/CV) charging. Above ~80%, current tapers to prevent overcharging and heat damage, extending the last 20% significantly.
For most consumer devices, 80-90% is realistic. Wireless charging is less efficient (60-75%). High-quality wired chargers can reach 90-95%.
Yes. Use the EV preset or enter your battery capacity in Wh and your charger\'s power in watts. Keep in mind that EV charging rates often vary with state of charge.