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Battery Capacity & Charge-Time Model Calculator

Estimate charging duration from remaining amp-hours and a fixed effective charging-current assumption.

  • Formula & worked example
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Calculator inputs

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How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Edit a calculated value to solve backwards, or lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

Private by default

Inputs and results stay in this browser tab. Bookify does not upload or store the values you enter.

Formula and method

A 38 Ah battery starting at 50% charge has 19 Ah remaining. At 10 A with the 95% lithium-ion model factor, the estimated charging time is two hours.

Estimated hours = capacity × (1 − state of charge ÷ 100) ÷ (charging current × model efficiency)

Worked example

Enter these known values and leave the other values blank.

Battery capacity
38 Ah
Charging current
10 A
Current state of charge
50 %
Battery model factor
Lithium-ion
Charge time
2 hrs

Assumptions and limitations

  • No. The model assumes constant current and fixed factors of 95% for lithium-ion, 85% for lead-acid and 70% for nickel-based options. Actual charging can taper and depends on the battery and charger controls. Use the manufacturer-approved charger and settings; this arithmetic estimate does not select them.
  • Match the units shown and use measured inputs where available. The result follows the stated model and does not account for unentered changes.

Common questions

Does this determine a safe charging current or a full-charge deadline?

No. The model assumes constant current and fixed factors of 95% for lithium-ion, 85% for lead-acid and 70% for nickel-based options. Actual charging can taper and depends on the battery and charger controls. Use the manufacturer-approved charger and settings; this arithmetic estimate does not select them.

References

The calculation equations, inverse formulas, units, and input rules were imported from this source. Bookify provides the interface and equation solver.

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