Battery Charging Time Calculator
Enter the battery capacity, the charger current, how much charge you need and a loss factor to estimate the charging time.
Reviewed by the WorldCalcs team · Methodology · Last reviewed: September 2026
Quick answer
Charging time
5.75hours
- Hours and minutes
- 5 h 45 min
- Total minutes
- 345 min
Hours = capacity (Ah) × charge needed ÷ 100 × (1 + losses ÷ 100) ÷ charger current (A)
This is an estimate only. Real charging time depends on the charger, the battery's age, state of health and temperature, and on the charging profile the charger uses. Always follow the battery and charger manufacturer's instructions. See our Disclaimer.
How the estimate works
A battery rated in amp-hours can, in principle, deliver that many amps for one hour. Turn it around and the same arithmetic gives charging time: the amp-hours you need to replace, divided by the amps the charger supplies.
Two adjustments make the number useful. The first is how much charge you actually need — a battery at 20% only needs 80% of its capacity put back. The second is charging losses: not every amp-hour from the charger ends up stored in the battery, because heat and gassing consume some of it. Lead-acid typically loses 10–20%, lithium-ion 5–10%, so the calculator multiplies by (1 + losses ÷ 100).
Why real charging takes a little longer
Chargers do not hold a constant current all the way to full. As the battery approaches full charge the current tapers off, so the last 10–20% of the charge takes disproportionately long compared with the bulk phase at the start.
That is why this calculator is a lower-bound working estimate. It is well suited to planning a shift or an overnight charge, and less suited to predicting the exact minute the charger will finish.
Worked example
Take a 500 Ah forklift battery that is 80% discharged, on a 100 A charger, with 15% charging losses.
The charge needed is 80% of 500 Ah, and the loss factor multiplies that by 1.15: 500 × 0.80 × 1.15 = 460 amp-hours to push in.
Divide by the charger current: 460 ÷ 100 = 4.6 hours. Expect a little longer in practice, because the charger reduces its current as the battery approaches full.
All calculations happen in your browser. Nothing is sent, stored, or tracked.
Results are estimates and may contain errors — for general information only, not professional advice. Always verify before relying on them. Disclaimer
How to use
Enter the battery capacity in amp-hours (Ah). It is printed on the battery label — for a forklift or traction battery it is the rated capacity, not the voltage.
Enter the charger current in amps (A). Use the charger's DC output current, which is the current that actually reaches the battery, not the mains current it draws.
Set how much charge is needed as a percentage of full capacity, and choose a loss factor. Lead-acid batteries typically lose 10–20% of the energy put in, lithium-ion 5–10%.
Read the estimated charging time in hours, with the same figure shown in hours and minutes underneath.
Frequently asked questions
Why add charging losses?+
Is this exact?+
Can I use this for a forklift battery?+
Amps, volts and ohms — how do they relate?+
Does charging from 50% take half the time?+
References
- Battery University — BU-403: Charging Lead Acid, batteryuniversity.com.
- Battery University — BU-409: Charging Lithium-ion, batteryuniversity.com.