Battery Electric Vehicle Charging Information

How do you compute power?

It’s a simple formula:
[crayon show-plain-default=”true” toolbar=”false” nums=”false” striped=”false” lang=”” title=””]
Amperage * Voltage = Watts
Honorable mention: There is some minor loss of voltage over distance based on cable gauge but that goes beyond this post. Tables below will be simple math assuming zero resistance and zero voltage drop.

What about power storage?

This is pretty straight forward.

[crayon show-plain-default=”true” toolbar=”false” nums=”false” striped=”false” lang=”” title=””]If the energy is being transmitted or used at a constant rate (power) over a period of time,
the total energy in kilowatt-hours is the power in kilowatts multiplied by the time in hours.

Go ahead and read the WikiPedia article.

And the formula to fill a battery is straight forward:
[crayon show-plain-default=”true” toolbar=”false” nums=”false” striped=”false” lang=”” title=””]
kW * hours = kWh
Example: If you have a 30kWh battery pack and you can charge at 6.6kW then it would take about 4.6 hours to charge from 0 to 100%.

Unfortunately this isn’t completely accurate. Electric vehicle batteries have a state of charge (or SoC). Once you plug it in it charges very fast from 0-80% and then the charge rate drops as it gets closer to 100%. Just like your cell phone.

What are normal usage rates?

Car wH/m m/kWh
Model S 275 3.64
Model X 316 3.16
Model 3 242 4.13
Bolt EV 252 3.97
18 Volt 347 2.88
17 Leaf 280 3.57
18 Leaf 267 3.75

From there you can calculate your time to charge based on your battery size. The table above would get unruly if I listed all the battery combinations.

Power to estimated miles per hour of charge

So here is a simple table of power outputs and I have included some samples of usage to miles per hour of charge. These are only estimates. Every vehicle uses different sized inverters and accept power at different rates and loss.

The rates below use summer time watt-hour (Wh) of usage per mile (or the reverse math if vehicle reports things in miles/kWh).

See table above for estimated usage rates used in the calculations below.

Amps Volts Power Model S [1] Model X [1] Model 3 [2] Bolt EV 18 Volt [3] 17 Leaf [4] 18 Leaf [4]
24 208 5kW 18 16 21 20 10 18 18
24 240 5.8kW 21 18 24 23 10 21 21
32 208 6.7kW 24 21 27 26 10 24 24
32 240 7.7kW 28 26 32 31 10 24 24
40 208 8.3kW 30 26 34
40 240 9.6kW 34 30 40
48 208 10kW 36 32
48 240 11.5kW 41 36
72 208 15kW 54 47
72 240 17.3kW 62 55

[1] 10kW onboard charger standard, 17.3kW charger in dual charger (2016 and later) and earlier models of the Model S supported up to 20kW (80Ax240v)
[2] Limited to 7.7kW on standard battery and 9.6kW on long range option
[3] 3.6kW onboard charger Link
[4] 6.6kW onboard charger upgrade Link


I hope this helps fill in some gaps or at least gives you an idea of what to expect.

The difference in 208v vs 240v doesn’t make a huge difference in the kW of power calculation.

The above are estimates and some loss will occur.

For example, at my home, I have a HPWC fed with 100A service (which is 80A max usable) for 19.2kW. I only know a few people with a vehicle that can support this (dual charger older Model S). My Model S is from 2016 and supports 48A service but it’s only a 10kW charger inside so while my delivery is [email protected] (11.5kW) my vehicle charges at the slightly lower 10kW rate (or ~36m/h). More than enough for my overnight charging needs.

Want free Supercharging for your Tesla Model S or Model X? Use my referral link:

Edit: Fixed Model X from 350Wh/m to 316Wh/m as bad initial math

Edit: Fixed power calculation early in the table because of transposing