A recent blog by Patrick Mannion on EDN has floated the suggestion that "In all probability current electric vehicles will have an actual expected range of 10% (or less) of the advertised life."  This (and those of you who think me an EV-pessimist may be surprised to hear me say this) is somewhat over stating the case!

Take a Nissan Leaf with a 24kWh battery pack, and a whole bunch of worst-case assumptions.

Let’s assume that 80% of that is allowed to be used, and that after 5-10 years of regular fast-charging, 70% of that capacity remains.  That gets us down to a usable 13.4kWh.

The worst-case scenario consumption scenario for an EV is arguably constant flat-out high speed driving.  This consumes a lot of energy, with no opportunity for brake-energy recuperation.  The limited top speed for a Leaf is 90mph.  I reckon to push a Leaf through the air at 90mph takes around 33kW of power.  Let's add on 3kW worst-case additional electrical loads (lights, heater, stereo at max etc.)  Total power consumption is now 36kW.  This means that 13.4kWh will last around 22 minutes at 90mph.  That will take you around 33 miles.  

So yes – a max-speed blast in an aging Leaf with high electrical loads could see you running out of juice in around 20 minutes, having covered a bit more than 30 miles.  However, this is still around 30% of the advertised range – NOT the 10% postulated in the EDN blog!

This is why EV top speeds are limited.  The Leaf has an 80kW motor.  Were it allowed to run flat-out continuously, at a consumption of 83kW (with our 3kW electrical loads), the “aged” battery would only last 13.4/83*60 = 10 minutes.  I reckon 80kW would push a Leaf to around 126mph flat out, giving it a range-at-top-speed of only 20 miles.

But that’s still ~20% of advertised range, not 10%.