I meant "not practical" in that all components must be solid or liquid and that the reaction yields charge movement and can be driven by applying a charge. AFIAK carbon meets none of these.Of course it is. We use carbon now, specifically because it's an excellent store of energy. That's what got us into this mess.If my memory is right you actually get the maximum energy from carbon, not lithium. It's just not practical to actually use.
Batteries are just combustion, but slowed down and made to run in both directions.
It's all just shuffling electrons around.