Electronic wristwatches come in all shapes and sizes. Some utilize batteries while others do not. But wait. How can that be? How can you have an electronic watch without some sort of battery? By utilizing a capacitor instead. Batteries and capacitors are similar in terms of function, but drastically different in how they perform that function.
Batteries and capacitors are often confused as being the same thing. They are anything but. The biggest difference between them is how they store energy. Their energy storage methods also determine how they discharge energy. That influences everything from discharge rate to power life.
How a Battery Works
A battery is essentially a case that contains a combination of chemicals and ions. If you were to buy USB rechargeable batteries from Utah-based Pale Blue Earth, you would be getting a product based on lithium-ion technology. Those batteries do not store electricity; they store potential energy in a chemical solution.
A lithium-ion battery is charged by running electrical current through it. That current forces the ions on the positive side of the battery to move through a chemical solution to the negative side. Once fully charged, all of the ions are at the negative side. There is no electricity stored in the casing.
Instead, there is a chemical substance capable of creating electricity. How does that happen? By allowing the ions to return to the positive side of the battery. As those ions pass through the chemical solution, a reaction takes place. That reaction generates electricity.
How a Capacitor Works
A capacitor is an electronic component that stores potential energy in an electrical field. Capacitors do not technically store electricity, but it is the closest possible thing to doing so. A capacitor’s electrical field receives potential energy from current running into it. That same field generates electricity as the capacitor discharges.
Though the end result is the same as a battery’s end result in principle, there are significant differences in practice. That is why both batteries and capacitors are used for different purposes.
Charging and Discharging
In terms of charging speed, capacitors have the advantage over batteries. They charge instantly, where batteries take at least an hour or two. This particular property is what makes the capacitor so attractive to watchmakers wanting to design state-of-the-art pieces that need no winding or battery power.
Where discharging is concerned, batteries have the edge. Their discharge rate is much slower than a capacitor’s. A fully charged battery can provide power for quite a long time. A capacitor cannot. Though capacitors do not discharge instantly, their rate of discharge is exponentially faster than batteries.
Energy density is another advantage of lithium-ion batteries. A single battery can store much more potential energy than a capacitor. That means you get more raw power out of your batteries.
Cheaper to Build and Implement
Despite how well capacitors work as energy storage units, there is a reason they are not more widely used: they are more expensive to design and build. By comparison, lithium-ion batteries are fairly cheap. A lower build cost combined with higher energy density just makes batteries more economically viable.
Capacitors certainly have their place. They are used throughout the electronics arena. But in the end, they simply cannot do what batteries do. Their energy density isn’t high enough and their discharge rate is too fast. On the other hand, they are ideal for applications that do not require high energy density or long-lasting power.
And now you know. Capacitors and batteries are not the same thing. They do similar things, but they do them in different ways.