Why does the last twenty percent take so long?

Cells accept less current as they fill. On a DC fast charger the rate can drop to a fraction of peak above eighty percent, which is why 10 to 80 is the quoted figure.

Why does the wall draw more than the battery receives?

Charging losses, typically ten percent, to heat in the charger and the battery. You pay for the wall figure and the car stores the smaller one.

Everydayvehicle

EV Charging Cost and Time Calculator

EV charging time and cost. Charging rate tapers sharply above about eighty percent, so the last twenty percent can take as long as the first sixty on a fast charger.

Also called: ev charge time calculator, electric car charging cost.

Charging time

3 hours 36 minutes

3 hours 36 minutes to go from 20% to 80% on a 7.4 kW charger. That is 24 kWh into the battery, 26.67 kWh drawn from the wall, costing 213.33. It adds about 144 km of range. Within the range where charging rate holds up reasonably well.

Energy into the battery

Energy drawn from the wall

26.67

Cost

213.33

Range added

144

Cost per 100 km

148.15

Time in hours

3.6

On charging above 80 percent

Within the range where charging rate holds up reasonably well.

How this is calculated

Method and background

How this is calculated

Energy needed is the capacity times the charge window, and time is that over charger power adjusted for efficiency. The taper is the part a linear calculation misses: lithium cells accept high current when relatively empty and much less when nearly full, so DC fast charging slows dramatically past eighty percent. That is why manufacturers quote 10 to 80 percent times rather than 0 to 100, and why charging to full on a road trip usually wastes more time than it saves.

the charge window matters as much as the charger, and rates taper sharply above about 80 percent

C: Battery capacity
P: Charger power

Worked examples

Each of these is asserted on every build. If a change to the engine ever moved one of these answers, the build would fail before the page could print it.

20 to 80 percent on a 7.4 kW charger

Battery capacity: 40 kWh
Starting charge: 20%
Target charge: 80%
Charger power: 7.4 kW
Charging efficiency: 90%
Electricity rate: 8
Efficiency: 6 km/kWh

Charging time3 hours 36 minutes

40 x 0.6; 24/0.9

Open this example

charging to full warns about the taper

Battery capacity: 40 kWh
Starting charge: 20%
Target charge: 100%
Charger power: 7.4 kW
Charging efficiency: 90%
Electricity rate: 8
Efficiency: 6 km/kWh

Charging time4 hours 48 minutes

boundary: past the taper point

Open this example

Method and limits

What it assumes

A constant charging rate, which holds for AC charging and not for DC fast charging.

What it deliberately does not model

DC fast charging tapers, so this understates the time to charge past eighty percent substantially.
Cold batteries charge more slowly until preconditioned.
The vehicle onboard charger caps AC charging regardless of the supply rating.

Formula version 1.0.0 · definition 1.0.0 · United States · Report a problem with this calculator

Frequently asked questions

Why does the last twenty percent take so long?: Cells accept less current as they fill. On a DC fast charger the rate can drop to a fraction of peak above eighty percent, which is why 10 to 80 is the quoted figure.
Why does the wall draw more than the battery receives?: Charging losses, typically ten percent, to heat in the charger and the battery. You pay for the wall figure and the car stores the smaller one.