It's because every battery has the same "amount" of energy as regards to capacity. The only difference between them is the rate at which they recharge, and how efficiently they divert power to your weapons system. Or, it takes more than twice as much energy for a heavy battery to open up a wormhole than a fast charge because of it's design. To maintain such a large capacity of energy, it needs to utilize technology that is better at storage, at the price of being weaker at dumping alot of energy at once. Either way it means the same thing; Fast charge batteries are better when you keep your energy mostly below 250, and Heavy charge batteries are more efficient when you keep your energy mostly above 250.

And? I don't think anyone understands the relevance of this mega...

What you're saying - "Fast charge batteries are better when you keep your energy mostly below 250, and Heavy charge batteries are more efficient when you keep your energy mostly above 250."

We're trying to come up with a system for battery disbursement and warping through wormholes because well, the current system doesn't make sense unless you revert to tricky word games.