# How batteries work

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1. Mar 21, 2016

### u0362565

Hi all,

For some reason I'm really struggling to understand how batteries store energy and how this relates to electric potential.

Can I just think of a battery as two separate plates one accumulating positive charges the other negative. The positive and negative charges are attracted but they are kept apart by the electrolyte? The only way for equilibration to occur or the electric potential to be converted to electrical energy is when the external circuit is formed between the battery terminals. At that point, electrons have an easy route to the positive terminal and the potential energy is lost on whatever load is in the external circuit? Is that about right? A bit like a hydroelectric dam where water is pumped up hill creating potential energy this is like the separation of unlike charges in the cell. When the dam is opened the waters potential energy becomes kinetic. In the batteries case the terminals are connected with wire and the electons flow losing their potential but the process is this in a constant loop until the battery drains.

2. Mar 21, 2016

### Eucliddo

Isn't it chemical energy that the battery initially stores? the positive and the negative plates/terminal are being separated by some chemical paste (lead) which is electrolytic. This chemical allows electrons to pass. The potential energy that you might saying must be the energy possessed by the electrons when they are not being used.

3. Mar 21, 2016

### ProfuselyQuarky

A battery is simply a component in a circuit that converts chemical energy into electrical energy by means of electrons. Under ideal situations, electrons can travel from one chemical to another. When the electrons move, they make an electrical charge that can powers things. In a battery, there are chemicals that can make the electrons create electric charge. However, there is a wall that forces the electrons (with the charges, positive and negative on either side) around the wires of the circuit to reach the other side of the battery. As it travels through the wires, it powers whatever is connected to the circuit (e.g. a light bulb, a fan, etc.). So, yes, your idea of a battery is correct. The electrolyte is the "wall" and the electrons have to go through the wires (the external circuit) to connect both the terminals. Does this help?

4. Mar 21, 2016

### Staff: Mentor

That's more like a capacitor, definitely not a battery.

To expand on the previous answers, a simple way to see a battery is that you take a chemical reaction and split it physically in two parts, to force the electron exchange that would accompany that reaction to take place via a wire.

5. Mar 21, 2016

### ProfuselyQuarky

Hmm . . . I never really grasped the main difference between a battery and capacitor aside from the fact that a battery stores chemical energy while a capacitor's potential energy is stored in a electric field. Don't they ultimately do the same things?

6. Mar 21, 2016

### Eucliddo

battery can be used as a voltage supply in a circuit while capacitor is used to store charge in an elecrric field. However, capacifor wouldn't work if you will not use AC SUPPLY.

7. Mar 21, 2016

### ProfuselyQuarky

Oh! So it doesn't work for a direct current? Thanks, Eucliddo.

8. Mar 21, 2016

### Eucliddo

yup. Capacitor is shorted in DC.

9. Mar 21, 2016

### davenn

NO

and NO again

Eucliddo has lead you well astray

yes they can both be used for supplying electrical energy to a circuit. the difference in in how they do that.
Capacitors are often used in electronics for supplying a small current to a circuit that is used to hold data/date time etc info
TV's VCR's, DVD, digital cameras, and a myriad of other devices for when batteries are changed, power cuts etc

A capacitor will only present a short circuit to a DC current during the brief time that it takes to charge up
Once equilibrium has been reached ie, the voltage across the capacitor rises to the supply voltage, current stops flowing into and out of the capacitor and the capacitor appears, as it's circuit symbol suggests, an open circuit
( NOTE, I didn't say through the capacitor ... very important difference)

A capacitor appears to be short circuit in an AC current as the current cycles and the current continuously flows into and out of each plate of the capacitor
( gives the APPEARANCE that current is continuously flowing through the capacitor)

Dave

10. Mar 21, 2016

### ProfuselyQuarky

Wow, thanks so much, Dave. This helps a lot. I appreciate it! I hope Eucliddo finds it helpful, too :)

11. Mar 21, 2016

### Eucliddo

DC is only used in charging capacitor. When capacitor is put in a circuit (ex. a cascaded amplifier circuit) and Vcc will be a battery, the capacitors will be ignored in computing gain because it's in the OPEN state (I was wrong earlier, Capacitor appears as shorted in AC not in DC). Capacitors need AC supply because it requires frequency which is absent in DC.

12. Mar 21, 2016

### Eucliddo

Mr. Dave's explanation is right so I guess that settles it. I was just trying to say earlier that unlike battery, capacitor cannot be used as a first-hand source. It still needs a voltage supply. Since it filters the input depending on the other components present.

13. Mar 22, 2016

### davenn

consider comparing it to a rechargeable battery, then both of them need an initial voltage supply to charge them up

once disconnected from that supply, they both can then be used as a voltage source
and in that situation, there is no real difference between them as a source.
The difference lies in how the source creates a potential difference
I gave examples for the use of a capacitor in that situation in my earlier post

Dave

14. Mar 22, 2016

### u0362565

Ok thanks for the comments, i think thats clearer. I found it hard to decipher electric potential and how this is created in a battery.

15. Mar 22, 2016

### Jeff Rosenbury

Capacitors make poor batteries, but sometimes (very rare) they are used that way.

An example is supercapacitors used to light emergency lighting in aircraft. The capacitor's advantage of not breaking down over years of service exceeds its disadvantage of providing relatively little power since it's only needed for a short time for emergency deboarding.

Mostly they are used for frequency adjustable impedance such as filters or DC blocking.

Batteries are much more complex if for no other reason than there are so many types. Fortunately there's the battery university.

16. Mar 22, 2016

### davenn

yes, but the situation has slowly been improving over the years

got a whole bunch of 10F 2.5V ones here if you want to experiment

17. Mar 25, 2016

### Staff: Mentor

A good battery design maintains an approximately constant voltage as you use it, for most of its capacity.
The biggest problem with using a charged capacitor to supply power is that its voltage inevitably must continuously fall as you drain current from it. So electronic circuits are usually required to compensate for this serious drawback.