More like 5-6%.  A quick googling yielded: <a href="https:&#x2F;&#x2F;www.eia.gov&#x2F;tools&#x2F;faqs&#x2F;faq.cfm?id=105&amp;t=3" rel="nofollow">https:&#x2F;&#x2F;www.eia.gov&#x2F;tools&#x2F;faqs&#x2F;faq.cfm?id=105&amp;t=3</a><p>Charging your battery might be less efficient.<p>They did the whole math in &quot;Sustainable energy without the hot air&quot;, and over all, even burning coal and using an electric car is better than burning petrol in a comparitively small engine.<p>Funny enough, a similar analysis applies for heating: burning natural gas to make electricity to drive a modern heat pump is more efficient than burning the gas directly for heat at the premises.<p>From a physical point of view, that&#x27;s possible because you only need low grade heat for your home, but burning gas produces high grade heat.