A lead-acid cell turns a chemical reaction into electric current. Use the buttons to look inside, then follow the electrons from the plates, out through the circuit, and back again when it charges.
A lead-acid cell is the basic unit of the oldest kind of rechargeable battery, still used in cars and backup power. One cell makes about two volts; several joined together make a 12-volt battery.
From outside it is a sealed plastic box with two terminals. The whole reaction that produces the electricity happens on hidden plates in acid, so cutting the casing open shows where the current really comes from.
The cell is filled with dilute sulfuric acid, the electrolyte. It soaks the plates and provides the medium in which the chemical reaction can take place and charge can move around inside the cell.
At the grey negative plate, made of sponge lead, the acid reacts with the lead and releases electrons. These electrons build up on the plate, making it the negative terminal, and are ready to flow out.
When an external circuit connects the terminals, the electrons leave the negative plate and travel through the wire, through the load (here a small lamp), and on toward the positive side. This flow of electrons is the current.
The electrons arrive at the brown positive plate of lead dioxide, where they are taken up in a matching reaction. Inside the cell, ions move through the acid to complete the circuit, so the whole loop keeps flowing.
Discharging leaves both plates coated with lead sulfate. Pushing current back in with a charger drives the reaction backwards, restoring the active material, so the cell can be used again and again.
A chemical reaction at the plates. The dilute sulfuric acid reacts with the lead, freeing electrons at the negative plate; those electrons travel through the external circuit while ions carry the charge inside the cell.
Each pair of plates makes one small cell. Stacking them alternately, with separators between, packs a lot of reacting surface into a small space, so the cell can deliver more current.
Dilute sulfuric acid both carries the ions that move charge inside the cell and takes part in the reaction at the plates. It is the medium in which the whole conversion happens.
They keep the positive and negative plates from touching. A touch would short-circuit the cell, so the separators let ions pass through while holding the plates physically apart.
Yes. Applying a charging voltage reverses the reaction, turning the lead sulfate back into active material on each plate, so a lead-acid cell can be discharged and recharged many times.