A cell is the basic power source in an electrical circuit. It’s a single unit that converts stored chemical energy into electrical energy, creating the push (voltage) that drives current through a circuit. The standard AA or AAA you drop into a remote control is a single cell, typically producing about 1.5 volts.
How a Cell Powers a Circuit
Inside a cell, a chemical reaction does the heavy lifting. The reaction separates electrical charges, building up negative charges at one terminal and positive charges at the other. This creates a difference in electrical energy between the two ends, called a potential difference or voltage. That energy difference is what pushes charges through whatever is connected to the cell: a light bulb, a motor, a speaker.
As charge flows through the circuit, it loses energy doing useful work (lighting the bulb, spinning the motor). When it returns to the cell, the chemical reaction pushes it back up to higher energy again, ready for another loop. Think of it like a water pump lifting water to the top of a hill so it can flow downhill and turn a wheel. The cell is the pump.
The voltage of a cell depends entirely on the chemistry inside it. A standard alkaline cell produces about 1.5V. A rechargeable nickel-metal hydride cell sits around 1.2V. Lithium-based cells range from about 2.4V to 3.7V depending on their specific chemistry.
What’s Inside a Cell
Every cell contains three essential components. The first is the negative electrode, which releases electrons into the external circuit during the chemical reaction. The second is the positive electrode, which accepts those electrons when they return from the circuit. The third is the electrolyte, a chemical medium (liquid, gel, or solid) that sits between the two electrodes and allows charged particles called ions to travel internally from one electrode to the other. This internal ion movement completes the circuit inside the cell while electrons travel the external path through your device.
Cell vs. Battery
People use “battery” and “cell” interchangeably, but technically they’re different. A cell is a single electrochemical unit with one set of electrodes and one electrolyte. A battery is a group of cells connected together. That rectangular 9V block you might use in a smoke detector actually contains six 1.5V cells stacked inside. A single AA, on the other hand, is genuinely just one cell, though everyone still calls it a battery.
A single cell is light and compact. It supplies a fixed voltage determined by its chemistry and a limited amount of total energy. Combining multiple cells into a battery lets manufacturers hit higher voltages or longer runtimes, depending on how the cells are wired together.
Primary and Secondary Cells
Cells come in two broad categories. Primary cells are the disposable ones: standard alkaline AAs, AAAs, coin cells in watches. Once the chemical reaction runs out, you throw them away. Secondary cells are rechargeable. Applying an external voltage reverses the chemical reaction, restoring the cell to its original state. The rechargeable lithium cells in your phone and laptop are secondary cells, as are the nickel-metal hydride rechargeables you can buy in AA size.
How Cells Combine in a Circuit
When you need more voltage than a single cell provides, you wire cells in series, connecting the positive terminal of one to the negative terminal of the next. The voltages add up. Two 1.5V cells in series give you 3V, which is exactly what happens inside a flashlight that takes two AAs stacked end to end. The total capacity (how long the cells last) stays the same as a single cell.
When you need longer runtime instead, you wire cells in parallel, connecting all the positive terminals together and all the negative terminals together. The voltage stays the same, but the capacity adds up. Two 12V cells rated at 100 amp-hours in parallel give you 12V with 200 amp-hours of capacity, meaning the system lasts twice as long before needing a recharge.
The total energy stored is the same whether you wire in series or parallel with the same number of cells. Series gives you higher voltage with lower current. Parallel gives you lower voltage with higher current capacity. Many real-world battery packs use a combination of both to hit a specific voltage and runtime target.
Internal Resistance and Real-World Voltage
A cell’s stated voltage is its ideal output, sometimes called its electromotive force or emf. In practice, every cell has some internal resistance caused by the materials and chemical processes inside it. When current flows, some energy is lost overcoming that internal resistance, so the actual voltage delivered to your circuit is slightly lower than the ideal value.
The more current you draw, the bigger the drop. Under light loads (like a wall clock drawing tiny amounts of power), the voltage is very close to the rated value. Under heavy loads, the delivered voltage falls noticeably. This is why a “dead” battery in a high-drain device like a camera flash might still work fine in a low-drain device like a remote control. The cell still has chemical energy left, but its voltage sags too much under heavy current to be useful.
The Cell’s Symbol in Circuit Diagrams
In circuit diagrams, a single cell is drawn as two parallel lines of different lengths. The longer line represents the positive terminal, and the shorter line represents the negative terminal. A battery (multiple cells) is shown as several of these pairs stacked together. If you see just one long-short pair in a diagram, that’s a single cell. If you see several in a row, that’s a battery.