Battery Charge Calculator: Charge Time, Amps and % Full

Calculate battery charge time from battery capacity, charger amps or watts, and start and target charge level, or find the charge level reached in a set time.

Solve for

Planning model only. Real charger current and voltage vary. Use battery and charger specifications; the modeled current is not a charging recommendation.

Charging model

Capacity rating

Rated charge capacity

Charger output rating

Charger current

Starting charge (%)

Blank uses 0%.

Target charge (%)

Blank uses 100%.

Optional settings

Nominal battery voltage (V)

Required for Wh ratings or watt-rated chargers. Otherwise optional for energy and cost.

Example charging assumptions

Examples set editable charge efficiency and taper values. They are not validated chemistry-wide curves.

Charge efficiency (%)

Stored Ah divided by charger Ah. Initial 95% is an editable example.

Taper starts at charge (%)

Initial 85% is a model assumption; real bulk charging ends at a voltage threshold.

Average taper current (% of bulk)

Initial 35% is an illustrative average, not a continuous CC/CV curve.

Example battery rating

Select deliberately to replace capacity and voltage. No charger setting is recommended.

Plug-in clock time

Optional. Shows an elapsed-time clock estimate using 24-hour days; no date or daylight-saving adjustment.

Electricity price (USD per kWh)

Optional. Requires nominal voltage for the energy estimate.

Overall energy efficiency (%)

Wall energy to stored energy. Initial 90% is an assumption separate from Ah charge efficiency.

Manufacturer current limit (A)

Optional datasheet limit for these conditions. Blank makes no limit comparison.

Battery Charge Formula

The equation below assumes ideal constant current, 0% to 100% charging and 100% charge efficiency. For a partial charge, multiply capacity by the required charge fraction and divide by charge efficiency. The calculator also offers an illustrative, editable bulk-and-average-taper model; real CC/CV charging follows the charger’s voltage and termination controls.

T = C / R

Where T is the total time (hours)
C is the battery capacity (charge) in mAh (or Ah)
R is the charge current in mA (or A)

To estimate charge time, divide the capacity by the charge current (use consistent units, such as mAh with mA or Ah with A). This gives an idealized value; many batteries and chargers take longer to reach 100% due to charge termination behavior (for example, lithium CC/CV taper near the top of charge).

Battery Charge Time Definition

Battery charge time (charging time) is the amount of time it takes a battery to reach a target state of charge (for example, from 0% to 100%) under a given charger and conditions. The time depends on charge current, battery chemistry, temperature, and the charger’s charging profile (for example, tapering near full charge).

Battery Charge Time Example

How to calculate battery charge time?

First, determine the total capacity.
Calculate the total capacity of the battery.
Next, determine the charge rate.
Calculate the average rate of charge.
Finally, calculate the time.
Calculate the charge time using the equation above.

FAQ

How long does it take to charge a battery?

The time it takes to charge a battery depends on the current being used to charge and the total size of the battery.

What is a battery capacity?

Battery capacity is the amount of electric charge a battery can deliver under specified conditions, commonly expressed in Ah or mAh. (Energy depends on voltage: Wh = Ah × V.)