Everything You Always Wanted to Know About EVs

…But Were too Embarrassed to Ask!

This thread is a safe place to ask those “stupid” questions that have been niggling away at you.

Let’s keep it short, succinct and on topic.


Here’s one to start…

kW or kWh?

kW is a measure of power.


The Peugeot e-208 has a 100 kW motor

50 kW Rapid Chargers are twice as powerful as 100 kW Rapids

kWh is a measure of capacity or consumption


The Peugeot e-208 has a 50 kWh battery

The Renault ZOE has an average consumption of 4 miles per kWh


Wh/mile or mpkWh

These are both valid ways of conveying EV efficiency or consumption. Many prefer mpkWh because it is very similar to mpg. You will though come across Wh/mile in forums and videos.

Wh/mile = watt hours per mile, or how many Wh you will use to travel 1 mile.

Example: 250 Wh/mile

mpkWh = number of miles you can travel using 1 kilo watt hour

Example: 4 mpkWh


(1/Whpm) x 1000 = mpkWh

(1/mpkWh) x 1000 = Whpm


1/250 x 1000 = 4
250 Whpm is equivalent to 4 mpkWh

1/3 x 1000 = 333
3 mpkWh is equivalent to 333 Whpm

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How about setting up a new category for Newbies to put all of this into? It would be easy to find and see all the other similar questions which are asked. I still have so many questions to ask too. Is that possible or would Onto need to make a new category available?

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Not sure. Perhaps @Lily_at_Onto could advise.

Battery Capacity: Total or Usable?

Manufacturers can be misleading when describing the battery capacity of one of their EVs.

For example, Nissan call the latest LEAF the 40, giving the impression that it has a 40kWh battery. In fact it has, but only 36kWh is available to the driver.

On the other hand, Renault claim the new ZOE 50 has a 52kWh battery. They are being clearer, because the battery can store a total of 56kWh, 52 of which are usable.

Why the difference? To protect the battery, manufacturers put a buffer at the top and bottom, so that an indicated 100% SoC is in reality maybe 95%. Equally at the bottom end, 0% would probably be 5%. This avoids the battery being kept at either completely full, or absolutely empty, both situations not conducive to long term battery health.

So when calculating how far you can go at mpkWh with your 45kWh battery, make sure you are using the usable figure and not the total one.

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And then BMW decide not to use KWh but Ah so the current I3, according to BMW, is 120 Ah which turns out to be 42 kWh, of which 38 kWh is accessible. It will allow you to use all of the accessible charge whilst the Tesla model 3 gets upset and tells you off if you charge to more then 90%.