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CHARGING TOOLS

Battery Charging Time Calculator

Estimate recharge time using battery capacity, the charge you want to restore, and compatible battery-side current. Distinguish a full-session average from a bulk-current estimate that may need extra finishing time.

MAKE IT YOURS

Your inputs

Starting values are examples. Replace them with the details for your setup.

Context only. Choosing a chemistry does not invent a charging profile.

Ah
%
%
A

Compatible battery-side charging current; not an adapter rating at another voltage.

%

Charge efficiency in Ah, not wall-to-battery energy efficiency.

min

A sourced or user-supplied allowance. Leave blank if taper/absorption time is unknown.

Use a compatible charger’s documented settings. Capacity alone does not determine a safe charging current.

Calculations stay in your browser.

EXAMPLE RESULT

Bulk charging-time estimate

6 h 40 min

Charge to restore
60 Ah
Constant-current estimate
6 h 40 min
Finishing allowance applied
0 min
Estimated total time
Undetermined without a finishing allowance

What this assumes

  • 10 A compatible battery-side charging current; 90% coulombic charge efficiency (Ah), not wall-to-battery energy efficiency.
  • Bulk/rated current does not establish full-charge time; absorption or taper may add an unknown amount.
  • Unspecified chemistry is context only; no chemistry-specific profile or recommended charger setting is inferred.

A share link includes the inputs used for this result.

How the calculation works

Ah to restore = capacity Ah × (target % − start %) ÷ 100. Estimated current-based hours = Ah to restore ÷ (battery charging amps × coulombic efficiency). Add a separate finishing allowance only when using bulk current, not a full-session average.

WORKED EXAMPLE

Example: a current-based estimate

For an illustrative 100 Ah battery going from 20% to 80%, restore 60 Ah. With an assumed compatible 10 A charging current and 90% coulombic efficiency, 60 ÷ (10 × 0.9) is about 6 hours 40 minutes. If 10 A describes only the bulk phase, this does not establish the full finishing time.

WORKED EXAMPLE

Example: an explicit finishing allowance

Adding a user-supplied 30-minute finishing allowance to that bulk-current example gives about 7 hours 10 minutes. The allowance is illustrative, not a universal battery rule. If the 10 A input already represents the true average over the complete charge interval, do not add taper again.

Coulombic efficiency tracks charge, not energy

Here, efficiency is retained amp-hours divided by amp-hours supplied during charging. It is distinct from the wall-to-battery energy efficiency used by the Tesla estimator. Adapter output current at a different voltage is not automatically the current entering the battery.

Charging current changes over a session

Lithium charging commonly includes constant-current and constant-voltage phases. A charger’s rated current is therefore not necessarily its full-session average. For bulk-current mode with no known finishing allowance, treat the output as a bulk estimate and the total time as undetermined.

Use compatible equipment and supported assumptions

Use current and charging guidance appropriate to the battery and charger. Capacity alone cannot determine a safe charger setting. A chemistry label supplies context; it does not load a manufacturer-specific charging curve or make this a starter-battery repair guide. An already-reached target requires no charging time or finishing allowance.

Sources & methodology

Technical guidance checked September 27, 2026. Example inputs are illustrative, not specifications for a particular vehicle or battery.