Charging Time Is Not a Single Division

The textbook formula — energy needed divided by charger power — describes a fuel pump, not a battery. A lithium-ion pack accepts power at a rate that changes continuously as it fills, so a session that averages 80 kW may have started above 150 and finished below 40. This calculator therefore simulates the session in one-percent increments, applying the acceptance rate appropriate to each state of charge, and sums the resulting times rather than dividing once.

Two Ceilings, and the Lower One Wins

Every session is limited by both the charger's rating and the vehicle's maximum acceptance rate, and only the smaller of the two matters. A car rated at 55 kW draws 55 kW from a 350 kW dispenser and the remaining capacity sits idle. This is the single most common source of disappointment at a fast charger, and it is why the vehicle's own rate is an explicit input here rather than an assumption. The result card states which of the two is binding.

Why the Curve Collapses Past Eighty Percent

Filling the last portion of a pack requires forcing lithium into an increasingly saturated anode. Doing so quickly risks metallic plating on the anode surface, which permanently reduces capacity, and generates heat the cooling system must remove. The battery management system responds by cutting current sharply, typically from around eighty percent. The practical consequence is stark: the final twenty percent of a fast-charge session often takes as long as the first sixty.

Temperature Gating Applies to DC, Not AC

A cold pack has slower internal chemistry and higher resistance, so the vehicle restricts DC current until its heater brings the cells into range — commonly a forty percent cut in peak power. Preconditioning on the approach to a fast charger largely removes the penalty. AC charging behaves differently: the onboard charger, not the pack, sets the ceiling at 7 to 11 kW, a rate low enough that a cold battery can accept it regardless. This calculator applies the temperature derate to DC sessions only.

Grid Energy Versus Battery Energy

The kilowatt-hours a charger meters are not the kilowatt-hours that reach the battery. Conversion, cabling and thermal management consume roughly ten to twelve percent on AC, where the onboard charger performs the AC-to-DC conversion, and five to eight percent on DC, where the conversion happens in the cabinet instead. Because the charger delivers grid-side power, timing is calculated against grid energy, while range added is calculated from the smaller figure that actually reaches the pack.

Planning Stops Around the Curve

On a long journey, total travel time usually falls when each stop is kept short. Charging from ten to sixty percent happens in the fast part of the curve; waiting from eighty to one hundred does not. Two brief stops in the steep region frequently beat one long stop that runs into the taper, even after accounting for the time lost pulling off the road twice. The Time Above 80% figure in the summary is there to make that trade-off explicit.

How Far to Trust the Estimate

The taper shape used here is representative rather than vehicle-specific; published curves differ by manufacturer, cell chemistry and even software revision, and a pack that has already been fast-charged twice that day will behave differently from a cold-start session. Expect agreement within roughly ten to fifteen percent under comparable conditions. That is close enough to choose between chargers and to size a stop, and not close enough to schedule against to the minute.