Why is the real charge time longer than expected?

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.

What\'s the difference between mAh and Wh?

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.

How do I find my charger\'s wattage?

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.

Why does charging slow down above 80%?

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.

Is 85% efficiency realistic?

For most consumer devices, 80-90% is realistic. Wireless charging is less efficient (60-75%). High-quality wired chargers can reach 90-95%.

Can I use this for electric vehicles?

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.

Battery Charge Time Calculator

Estimate how long it takes to charge a battery from any percentage. Supports phones, laptops, EVs, and power tools with efficiency accounting.

Battery Capacity

Unit

Voltage

Charger Power

Current %

Target %

Charging EfficiencyTypical: 80-90%. Energy lost as heat.

Charge Time

2h 21m

141.2 total minutes

Energy Needed

20.00 Wh

23.53 Wh with efficiency loss

Battery Capacity

25.0 Wh

Total energy capacity

Charger Current

2.00 A

At 5V

Energy Lost as Heat

3.53 Wh

15% efficiency loss

% Per 10 Min

+5.7%

Average charging rate

Charge Progress Estimate

Battery %	Time Elapsed	Bar
30%	18m
40%	35m
50%	53m
60%	1h 11m
70%	1h 28m
80%	1h 46m
90%	2h 4m
100%	2h 21m

Planning notes, formulas, and examples

About the Battery Charge Time Calculator

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.

When This Page Helps

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.

How to Use the Inputs

Select a preset or manually enter your battery capacity (mAh or Wh).
Enter the battery voltage (check device specifications).
Enter your charger\'s power rating in watts.
Set the current battery percentage and target percentage.
Adjust charging efficiency (80-90% is typical).
Read the estimated charge time and progress timeline.

Formula used

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

Example Calculation

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.

Tips & Best Practices

Higher-wattage chargers aren\'t always faster — the device limits the intake.
Charging to 80% instead of 100% is faster and better for battery longevity.
Wireless charging typically has 60-75% efficiency — adjust accordingly.
The EV preset uses typical Level 2 home charging values.
Use the "% per 10 minutes" output to gauge if a quick charge is worth it.
Heat reduces efficiency — charge in cool environments when possible.

Understanding Charging Efficiency

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.

Fast Charging Technologies

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.

Battery Health and Charging Habits

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.

Sources & Methodology

Last updated: June 1, 2026

Frequently Asked Questions

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.