Only have a german source that did the math
https://sedl.at/Elektroauto/Energieeffizienz
Money quote:
"Selbst wenn wir die Betrachtung auf den gesamten Lebenszyklus der Fahrzeuge und alle vorgelagerten Aufwände ausdehnen, schneidet ein Elektroauto
ungefähr gleich wie ein herkömmliches Auto ab. Wegen des gewaltigen Energieaufwands bei der Herstellung von Lithium-Akkus allerdings nur dann, wenn das Elektroauto max. 150 km Reichweite hat (damit es keinen großen Akku braucht) und mindestens 100 000 km mit dem gleichen Akku gefahren wird. Für Gelegenheitsfahrer ist die Herstellung des über hundert Kilogramm schweren Stromspeichers zu energieintensiv. Vgl.
Kohlendioxid-Ausstoß von Elektroautos"
Which means: They are comparable but only if the battery has a range of less than 150km or else it is too heavy to be efficient.
Also the production cost of the battery sells of at 100000km.
There is also the interesting note that efficienty drops very heavy in winter:
"Bei einer Außentemperatur von 22°C mit eingeschalteter Lüftung beträgt der Wirkungsgrad vom Akku bis zur Straße 56%, bei –5°C und eingeschalteter Stromheizung nur 22%."
So you drive with 44% energy loss in summer and 78% energy loss in winter. Numbers for a brand new car in a test chamber!
A conventional car is quoted with 70% loss but there are no citations for that.
Edit: on other pages he also cites the efficience goes down with heat too, so thats not summer but driving at "room temperature".
And of course the oblicatory wikipedia link on how to produce methane.
https://en.wikipedia.org/wiki/Power-to-gas
That page states the loss of turning power to methane with 35%, on top of that comes the 70% loss statet above. Engines burning methane should be more efficient than that tho.
This is all more or less the same range, basically the power used for driving is more depending on the air pressure in the tires than the engine. I droped from 5€ to 4€ per 100km by just inflating my tires up to 3 bar.
I just doubt its worth making the batteries when you dont gain a thing here. And spare me this "but your car is polluting the air" crap, my CNG burns extremely clean, not even closely comparable to liquid gas.
And if you have not noticed: The power to gas method creates giant air cleaners as a side effect.
Edit: Not limited to CNG cars when further processed
https://en.wikipedia.org/wiki/Gas_to_liquids