Nuclear fission reactors are even crazier. With breeding you get 22,500,000,000 Wh/kg. Good old E=MC^2.

Technically all batteries are E=mc^2, it's just that nuclear fission converts more of the mass, but still, not all of it.

Lithium batteries do get ever so slightly heavier when charged, but it's basically undetectable.

How do lithium ion batteries convert mass to energy?

The principle of E=mc^2 is of mass-energy equivalence. Any form of stored energy has mass, including the binding energy between atoms in a molecule, and lithium ions convert those chemical bonds to electric currents when a load is applied.

The mass associated with those chemical bonds is miniscule compared to the protons, electrons, and neutrons, but it is not zero.

All (confined?) energy is equivalent to mass, even when that mass isn’t in the form of elections and quarks.

There's a really good joke about Ferengi political situations here, but I'm no economist.

I think quark jokes are a bit cheesy myself. ;)

I find them strange and charming

Hey it is not Reddit, but at least these are not off-color jokes.

Fission is not anywhere near E=MC^2. That would be matter/antimatter annihilation.

It is E=MC^2 though. 0.1% of the mass is converted into energy.

Windup toy cars are also E=mc^2.

E = mc^2 implies that mass (m) is being converted to energy (E), and a windup toy car is definitely not converting mass to energy. Windup cars get their energy from torsional springs, which are E = (1/2) k theta^2.

>and a windup toy car is definitely not converting mass to energy

Ah, but it is. E=mc^2 is always true in the reference frame where the object is stationary. (We assume that we are co-moving with the windup car.) A spring under torsion is heavier than an unwound spring.

> A spring under torsion is heavier than an unwound spring

Does it have more (invariant) mass?

Yes.

No, it's E=(0.001M)C^2

That is absurd. It is E=MC^2 where M is 0.1% of the total mass of the reactants.

100% of the mass difference is converted into energy.

The GP was talking in relation to W/Kg, and the output per Kg is definitely not e=mc^2. It helps reading things in the context.

You are correct, though it would help to clarify that you're correcting the GP on the "per kilo" part, and not the "energy" part.

I agree, if you're deploying 1 kg of fissile material, only 0.1% of that will be converted to energy. We should talk about energy per mass of fissile material, not energy per mass of "mass difference".

So with a nuclear fission reactor NASA could make an immortal space probe! It's very sad that this isn't a project.

Nuclear fission reactors have a lot of moving parts, and creating something that lasts 50 years without one of those moving parts failing, unmanned, and subject to the harshness of space, isn't trivial.

Nuclear batteries are extremely reliable though, as they are fully solid state. A Pu-238 battery can emit useful amounts of power for upwards of a century, and there is virtually nothing to break.

The Russians have a few of those: https://en.wikipedia.org/wiki/BES-5

It appears to be holding up well at 27 years past the age spec too. It is astonishing how something sent out when I was a toddler is still working till this date; kudos to the engineers.