Battery Charge Time Calculator

Estimate how long a battery takes to charge from a solar array or charger.

About Battery Charge Time Calculator

Charging is at full power only up to roughly 80 per cent state of charge, after which the current tapers to protect the cells. The bulk phase figure is the practically useful one. Solar charging power varies through the day, so real charge times are longer than a fixed-power calculation suggests.

Formula

Battery Charge Time

Time = energy to replace ÷ (charge power × efficiency)

bulk phase: Constant-power charging to about 80%, after which the rate tapers

Worked example

With the default values below, Battery Charge Time Calculator returns Charging Time of 2.899. Change any input above and every figure here is recalculated in your browser.

Inputs used

Battery capacityminimum 0 kWh: 10 kWh
Starting state of chargeaccepts 0–100 %: 20 %
Charging power availableminimum 0.01 kW: 3 kW
Charging efficiencyaccepts 0–100 %: 92 %

Results

Charging Time: 2.899 h
Energy to Replace: 8.000 kWh
Time to Reach 80 Per Cent: 2.174 h
Charging Time: 173.9 min
Effective Charge Rate: 2.7600 kW

Step by step

1Values used
2Battery Charge Time
3Charging Time= 2.899 h
4Energy to Replace= 8.000 kWh
5Time to Reach 80 Per Cent= 2.174 h
6Charging Time= 173.9 min
7Effective Charge Rate= 2.7600 kW

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax or compounding frequency into account.
Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is Battery Charge Time calculated?

Time = energy to replace ÷ (charge power × efficiency) Charging is at full power only up to roughly 80 per cent state of charge, after which the current tapers to protect the cells. The bulk phase figure is the practically useful one.

Why does Battery Charge Time matter?

Solar charging power varies through the day, so real charge times are longer than a fixed-power calculation suggests.

What values do I need to enter?

This calculator takes 4 inputs: Battery capacity, Starting state of charge, Charging power available, Charging efficiency. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.