Estimate EV charging time by power.
Charging time is the energy the battery needs divided by the rate at which the charger can deliver it, with two corrections. First, losses mean more energy passes through the charger than reaches the cells, so the metered figure is what the power rating has to move. Second, DC rapid charging tapers sharply above about 80 percent state of charge to protect the cells, so a session that crosses that point averages well below the charger's headline power — modelled here as a quarter reduction on chargers above 22 kW.
Energy required
kWh needed = capacity x (target SoC - current SoC) / 100 / (1 - loss)
Duration
Hours = kWh needed / effective charger power
Charge acceptance falls as the cells fill, so the battery management system cuts current to limit heat and lithium plating. On many cars 10 to 80 percent takes about as long as 80 to 100.
For a large top-up, yes — 40 kWh at 7.4 kW is roughly six hours. That is usually fine, because the car is parked for far longer than it needs, and off-peak tariffs make the slow rate an advantage.