That gravimetric energy density is about 2 orders of magnitude higher than lithium ion batteries.
To be fair, high gravimetric density is a fairly large advantage for an air plane. But the bad volumetric energy density does present some serious challenges.
It can be part of the main propulsion.
Most internal combustion engine cars have a lead acid battery to start it up and run the spark plugs (or preheat the glow plugs if diesel). They don't get called "hybrid" or "battery powered" because the batteries aren't the propulsive power themselves.
This is akin to that: the batteries run the pumps, they're not the propulsive system itself.
Ion drives can be run off battery, but you can't launch with those.
That's about 0.3% of all energy generated by the engines, which is significantly more than what a spark plug does in an ICE.
[1] https://theaeroblog.com/the-rutherford-rocket-engine-the-fir...
This is the closest we have to electric power directly powering the ascent of a rocket from Earth.
Something like a HyperCurie engine (which is also electric pump-fed), could probably lift off from a planetary body like the moon. When they used it in orbit, they actually had to wait for the batteries to charge up from solar panels between each engine burn.
> 0.3%
> the closest we have
I don't understand why you're trying to paint the battery as a significant contribution here.
Like a car battery, although it's neat that they consider it as part of the engineering, it's none of the actual thrust unless it explodes.
It is all semantics anyway.
I'd agree "it's all semantics", but yours are confusing me :P
(And for energy content, like for like is comparing the size of the fuel tank with the capacity of the battery, but cars aren't 90% fuel by weight).