Updated Electronics & Power

Charge Time Calculator – Battery, Fast Charging & Runtime

Estimate charge time and runtime for phones, laptops, power banks, e-bikes and EVs. Use mAh and amps or Wh and watts, model fast-charging taper, compare chargers and see how long a battery can power a load.

Battery Capacity Inputs Charger Power & Efficiency Fast-Charging Taper Model Charger Comparison & Runtime

Interactive Charge Time & Battery Runtime Calculator

Use the tabs to calculate charge time from battery capacity and charger current, from energy in Wh or kWh and charger power, simulate fast-charging taper, compare two chargers for the same battery and estimate how long a device can run on a given battery.

Typical USB charging efficiency is around 80–90% once cable and device losses are included.

This mode assumes roughly constant charging current and is ideal for small batteries such as phones, tablets, power banks and other mAh-rated packs. Real devices may slow down near 80–100% for battery health, so actual times can be slightly longer, especially for the final part of the charge.

Use this mode for laptops, e-bikes, home battery systems and EVs where capacity is given in Wh or kWh and charger power is in W or kW. It focuses on a specific charge window (for example, 20% to 80%), which is more realistic and kinder to the battery than always using 0–100%.

Fast-charging usually slows down past 70–80% to protect the battery.
Approximate average power used after taper start, as a percent of rated power.

This mode splits the charge into two phases: a faster bulk phase up to the taper start level and a slower phase from there to the target level, using a reduced average power. It is a simple way to approximate real fast-charging behavior.

This mode compares two different chargers or ports for the same battery or pack. It reports charge time for each and the time saved by using the faster option, which is useful for EV charging choices, laptop adapters and USB-C PD chargers.

Accounts for inverter losses and the fact that you rarely use 100% of the battery.

This mode estimates how long a given battery can power a device or system at a roughly constant average power. It is useful for UPS systems, home backups, campers, off-grid setups and general energy planning.

Charge Time & Runtime Calculator – Understand How Your Battery Behaves

Whether you are charging a phone, a power bank, a laptop, an e-bike or an electric car, one of the first questions is: “How long will it take?” The next question is often “How long will it run?” This Charge Time Calculator suite from MyTimeCalculator helps you answer both, using simple inputs that match common specifications on devices and chargers.

The calculators are built around basic energy relationships: amp-hours and watt-hours describe how much energy a battery can store, while amps and watts describe how fast that energy flows. By combining these with start and target state of charge and realistic efficiency values, you get practical estimates of charge time and runtime.

How the Charge Time Suite Is Organized

The tool is split into five modes to cover the most common scenarios:

  • Battery (mAh & amps): For phones, power banks and other small packs rated in mAh.
  • Energy (Wh / kWh & watts): For laptops, e-bikes, home storage and EVs rated in Wh or kWh.
  • Fast-Charging Estimator: Adds a simple two-phase taper model at higher state of charge.
  • Charger Comparison: Compares two chargers or ports for the same battery.
  • Battery Runtime: Estimates how long a battery can run a device at a given average power.

Mode 1 – Charge Time with mAh & Amps

This mode is tailored to small batteries where capacity is given in milliamp-hours and chargers are labeled in amps. The calculator:

  • Converts mAh to Ah.
  • Scales capacity for the chosen start and target state of charge.
  • Divides by the effective current (charger current × efficiency).

The results include the charge time in hours and in hours-and-minutes, the effective C-rate, and the percentage of the battery filled during this session.

Mode 2 – Charge Time from Wh / kWh & Watts

Larger batteries are usually specified in watt-hours or kilowatt-hours. In this mode, the calculator:

  • Converts capacity to Wh internally.
  • Computes the energy associated with the selected percentage window.
  • Divides by the effective charger power (rated power × efficiency).

This is especially useful for EVs, where you may care about 20–80% instead of 0–100%, and for home battery systems where usable capacity is only part of the nameplate rating.

Mode 3 – Fast-Charging Estimator

Fast charging rarely happens at full rated power all the way to 100%. Most systems deliver a high power level until the battery reaches a certain state of charge, then taper down to protect the cells. The fast-charging estimator approximates this behavior with two phases:

  • A bulk (fast) phase from start percentage up to the taper start level.
  • A slow phase from taper start to the target percentage with reduced average power.

You control the taper start percentage and the slow-phase power as a percentage of rated power. The calculator then estimates the time spent in each phase and totals them.

Mode 4 – Charger Comparison

When you have multiple charging options – for example, a slower home charger and a faster public charger – the comparison tab helps you quantify the difference. For the same battery and percentage window, you enter:

  • Battery capacity and unit.
  • Start and target state of charge.
  • Charger A power and efficiency.
  • Charger B power and efficiency.

The calculator produces a table of charge times and a short summary of how much time you save with the faster option.

Mode 5 – Battery Runtime

Runtime is the flip side of charge time: given a certain amount of stored energy and a constant average load, how long will it last? This mode:

  • Converts battery capacity to Wh.
  • Applies an efficiency or usable-capacity factor.
  • Divides by the average load power in watts.

The result is shown in hours, hours-and-minutes and days, which is especially helpful for backup systems, off-grid setups and long-running devices.

Why Efficiency & Percentage Windows Matter

A simple “capacity ÷ power” calculation assumes perfect efficiency and full 0–100% charging or discharging. In reality:

  • Efficiency losses in chargers, inverters and battery management systems reduce usable energy.
  • Battery health is often better when staying within a middle range (for example, 20–80%).
  • Charging profiles frequently taper at high state of charge, slowing down the final part of the charge.

By explicitly setting efficiency and state-of-charge windows, you can match the calculator to your real-world usage and get more meaningful estimates.

Tips for Using the Charge Time & Runtime Calculator

  • Read capacity from the device label or spec sheet (mAh, Wh or kWh).
  • Use the charger’s rated current or power as a starting point, but remember that the device may limit it.
  • Choose an efficiency between 80–95% if you are unsure; refine it with real-world measurements if needed.
  • For everyday use, focus on partial charges rather than repeated 0–100% cycling.
  • For runtime planning, consider average load rather than short peaks or idle periods.

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Charge Time & Battery FAQs

Frequently Asked Questions About Charge Time & Runtime

Before you rely on a specific charger or battery setup, review these quick answers.

Real devices use charging profiles, thermal limits and safety margins that vary power during the session. The calculator uses a simplified model with average power and efficiency, plus an optional two-phase taper model. That makes it useful for planning, but exact times can still differ in practice.

Yes. The mAh & amps tab is ideal for phones, power banks, handheld consoles and many other USB-charged devices. Enter the battery capacity from the specs, your charger current and a reasonable efficiency value to get a quick estimate.

Faster charging generally produces more heat, which can age batteries more quickly. Modern devices manage this automatically, but many manufacturers still recommend avoiding repeated full-speed 0–100% charges for maximum lifespan. When in doubt, follow the device maker’s guidance.

If you are not sure, values around 85–90% are reasonable for many consumer chargers. Large battery systems and EVs may have different typical efficiencies; manufacturer documentation or community data can give more precise numbers. You can also adjust the efficiency slider until the calculator matches times you observe in real life.

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