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Setting: In a fantasy setting much like World of Warcraft (where huge liberties are taken regarding the level of technological sophistication), an evil emperor rules from a castle in which there are massive channels of flowing water. These channels are decorative, although the throne room contains a pool big enough to swim in.

Scenario: One day, for one reason or another, this emperor decides he needs a way to store massive amounts of electricity for use in one of his dastardly plots. He brings in the world's brightest alchemist and burdens him with the task.

I would really like it if the alchemist could basically turn the castle's decorative channels into a giant battery. He'd fill them with the necessary chemicals and components, then wire up a giant lightning rod on the top of the castle, which, when struck, would channel the electricity down into these pools where the electricity gets stored.

Question: Using the materials available in this quasi-advanced fantasy world, where the concept of a battery might already exist in some form, what would it take for this Giant Castle Battery to be even remotely "believable"? What would this alchemist have to do?

As should be clear by now, I have no real idea how batteries work. To wit, as an added bonus I would like it if the evil emperor could throw his enemies into the toxic pool as a means of painfully killing them.

Thoughts?

Thanks for your consideration!

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    $\begingroup$ Honestly, a World of Warcraft style setting takes a lot of liberties with physics. The scenario you described would be perfectly fine so long as you don't try to explain it too much $\endgroup$ – Andon Mar 23 '17 at 2:17
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    $\begingroup$ Passes the smell test to me. Well, actually if its a lead-acid battery, I pass out on the smell test. $\endgroup$ – kingledion Mar 23 '17 at 2:20
  • $\begingroup$ As someone who's had a close call with leakage from a SLA battery -- it'd take a while. :P $\endgroup$ – Shalvenay Mar 23 '17 at 3:19
  • $\begingroup$ @Shalvenay well, technically if it was leaking it's not a sealed lead acid battery anymore. $\endgroup$ – JDługosz Mar 23 '17 at 8:26
  • $\begingroup$ Go read a basic article on batteries. Power depends on the area of plates. Capacity depends on mass of plates and solutions. $\endgroup$ – Sherwood Botsford Mar 24 '17 at 19:08
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Not really…

A battery consists of plates of materials (e.g. metal) with different affinity for holding electrons. So given the chance, the electron in one would rather be in the other. The fluid provides for ion transport and the needed atoms to support a chemical reaction at each electrode. You can read up on the construction details of the first successful batteries and use that for your story.

The solution may very well be an acid, in some designs.

But there are a few problems. First, the battery will have plates of different material closely spaced together. You want a small gap between them filled with the electrolyte solution. A bigger separation will reduce its efficiency. So a battery won't have an electrode on opposite sides of a bathtub, but a series of plates like slices of bread filling the tub. There's no room to add a body.

So, you design it for intimidation, not just for use as a battery. Maybe you have a reservoir of the electrolyte separate from the chamber with the plates. The addition of a body will ruin the acid, contaminating it and consuming the properties it needs to make a good battery. Some acids don’t like water at all!

If you made the plate chamber extra deep so there was a foot or two of liquid above the plates, you definitely would not want to throw a body in there! The debris would slip between the plates and short out or otherwise ruin the cells.

In short, using your battery in such a manner will destroy it.

Second, lightning is not useful for charging a battery. And this simple design is not going to be rechargeable anyway: it consumes the plates and/or liquid as it produces power, and that’s not effectively reversed if you try and force electricity the other way.

Even if you did have a rechargeable battery, you need a voltage slightly higher then what the battery produces, held for hours. That's not the behavior of lightning.

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The most likely battery chemistry would be lead-acid. Fully charged the electrolyte contains sulphuric acid. Uncharged it would be just water.

Not sure how lethal this bath would be, but since the goal is torture not instant death, it should work just fine. The sulphuric acid would react with the eyes, mucuous membranes, and the lungs. I can't imagine this could possibly be pleasant. You'd probably want the concentration to be fairly low, so victims could enjoy their bath longer.

Storing energy from lightning in a battery is probably not that practical, though. I am not sure what low tech solution would prevent the energy from discharging as fast as it is charged. Magic high current diodes?

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