The well known "lemon battery" uses an acid to dissolve zinc and release electrons which flow back into the solution to form hydrogen gas.
These batteries are quite weak by comparison to store bought batteries, but it can be a useful learning tool.
Why are these batteries weak? In part, it is due to the chemical reaction and metals, but I wanted to squeeze every bit out of this battery concept by reducing the distance between zinc and copper, and increasing the surface area of both. To do this, I created stranded, coiled, wire and used a shoelace as a barrier between the metals, also serving as a permeable substrate for the electrolyte, vinegar.
Three cells in series produced 2.4V and illuminated a small LED, although current was very low. Production of hydrogen gas was very noticeable.
I wanted to share these methods with you in the hopes that this construction technique inspires other projects.
I was particularly fond of the lemon battery instructable by madaeon linked here: https://www.instructables.com/id/The-micro-Lemon-Battery-reusable-1-hour-of-led-l/
Step 1: Materials and Tools
The battery needs Zinc, Copper, and an acid.
For the zinc, I researched online and found that galvanized metal should be coated in zinc. Unfortunately, the wire packaging doesn't directly state that it is zinc, but I think it is. Galvanized steel wire functions as a source of zinc.
Copper wire can easily be found in most craft and hardware stores.
I chose to use white distilled vinegar for the acid, because there aren't any additional molecules of sugar or salt to think about.
To keep the two types of wire close but not directly touching I suggest shoelaces. They will absorb the electrolyte, but maintain a small distance between the metals.
For tools: I needed scissors, wire cutters, an electric drill, and a C-clamp.
Step 2: Creating Stranded Wire
Take about 20 feet of wire and loop it around your clamp. Insert the two free ends into the chuck of your electric drill and tighten them down. Spin the wires together to form stranded wire. Repeat with both wire types.
Strand the copper wire an additional two times to thicken it up. This will become the core of our hollow shoelace.
Step 3: Coiling the Wires Into a Cable
Cut one end of the shoelace and insert the thicker copper stranded cable into the hollow shoelace.
Push the copper cable all the way in, hopefully you have some excess at the end, otherwise you'll need to keep some exposed so you can make an electrical connection later.
Begin wrapping the galvanized cable around the shoelace with copper core. Wrap the entire thing until you reach the end.
Now, we have a large amount of zinc and copper ready to react with very little distance between them, but not touching. The shoelace will absorb the acid.
To save space, over coil the cable in on itself or wrap it around itself. You can be as creative as you like here, just remember that the exposed copper and one end of your galvanized wire are our connection leads to measure the voltage.
Step 4: Electrical Tests
As you can see from the images, without any acid, the coils produce no voltage. Once the acid is added, each cell produced ~1 volt and all three in series produced > 2 V.
In the closeup image, note the gas bubbles rising. This is hydrogen gas, and these coils produced a lot of it, continuously. There could be a project in here...
Lastly, check the multimeter set to current measurement. This is the current in a short circuit. Max, 40 micro Amps. I was able to illuminate a blue LED with these three cells as a battery.