Battery types, characteristics and reactions

Batteries can generally be purchased insulated; but, they are also achieved coupled with each other in series or parallel, the set of which comes to be what they call batteries. And so it is that sometimes the terms ‘batteries’ and ‘batteries’ are used indiscriminately, even when they are not the same.

Alkaline batteries: one of the most popular types of batteries

Stacks can come in countless colors, shapes, and sizes, just as they can be made from other materials. Also, and more importantly, its internal structure, where the chemical reactions that generate electricity take place, serves to differentiate them from each other.

Battery classification

Before addressing some of the different types of batteries out there, it is necessary to know that these are globally classified as either primary or secondary.

– Primary batteries

Primary batteries are those that, once consumed, must be discarded or recycled, since the chemical reaction on which the electric current is based is irreversible. Therefore, these cannot be recharged.

They are mainly used in applications where it is impractical to recharge electrical power; such as in military devices, in the middle of the battlefield. Also, they are designed for equipment that consumes little energy, so that they last longer; for example, remote controls or portable consoles (such as Gameboy, Tetris and Tamagotchi).

Alkaline batteries, to cite another example, also belong to the primary type. They usually have cylindrical shapes, although this does not imply that cylindrical batteries cannot be secondary or rechargeable.

– Secondary batteries

Unlike primary batteries, secondary batteries can be recharged once they have run out of power.

This is because the chemical reactions that occur within them are reversible, and therefore, after applying a certain voltage, it causes the product species to become reactive again, thus starting the reaction again.

Some secondary cells (called batteries) are usually small, like the primary ones; however, they are intended for devices that consume more energy and for which the use of primary batteries would be impractical economically and energetically. For example, cell phone batteries contain secondary cells.

Also, secondary cells are designed for large equipment or circuits; for example, car batteries, which are made up of several batteries or voltaic cells.

They are generally more expensive than primary cells and batteries, but for long-term use they end up being a more suitable and effective option.

– Other aspects

Stacks are classified as either primary or secondary; but commercially or popularly, they are usually classified according to their shape (cylindrical, rectangular, button-type), the intended device (cameras, vehicles, calculators), their names (AA, AAA, C, D, N, A23, etc. ), and their IEC and ANSI codes.

Likewise, characteristics such as their voltage (1.2 to 12 volts), as well as their useful life and prices, are responsible for giving them a certain classification in the eyes of the consumer.

List of battery types

– Carbon-zinc batteries

Zinc-carbon battery illustration

Carbon-zinc batteries (also known as Leclanché cells or saline batteries) are one of the most primitive, and are currently considered almost in disuse compared to other batteries; in particular, compared to alkaline batteries, which although they are a bit more expensive, have a higher life time and voltages.

As its name suggests, its electrodes consist of a zinc can and a graphite rod, corresponding to the anode and cathode, respectively.

In the first electrode, the anode, electrons originate through the oxidation of metallic zinc. These electrons then travel through an external circuit that supplies the device with electrical energy, and then end up at the graphite cathode, where the cycle is completed by reducing the manganese dioxide in which it is immersed.


The chemical equations for the reactions that occur at the electrodes are:

Zn (s) → Zn 2+ (ac) + 2e –    (Anode)

2 MnO 2 (s) + 2e  + 2 NH 4 Cl (aq) → Mn 2 O 3 (s) + 2 NH 3 (aq) + H 2 O (l) + 2 Cl  (aq) (Cathode)

These batteries are very similar to alkaline batteries: both are cylindrical (such as the one in the image). However, carbon-zinc batteries can be distinguished by reading the characteristics labeled on the outside in detail, or if their IEC code is preceded by the letter R. Their voltage is 1.5 V.

– Alkaline batteries

Alkaline batteries are very similar to the carbon-zinc type, with the difference that the medium where the electrodes are located contains OH  anions . Said medium consists of strong electrolytes of potassium hydroxide, KOH, which contributes the OH  that participate and “collaborate” in the migration of electrons.

It comes in different sizes and voltages, although the most common is 1.5V. They are perhaps the best known batteries on the market (Duracell, for example).

The reactions that occur at your electrodes are:

Zn (s) + 2OH  (aq) → ZnO (s) + H 2 O (l) + 2e   (Anode)

2MnO 2 (s) + H 2 O (l) + 2e  → Mn 2 O 3 (s) + 2OH  (aq) (Cathode)

As the temperature increases, the faster the reactions occur and the faster the batteries discharge. Interestingly, popular rumors spread to put them in the freezer to increase their life span; but, when cooled, its content can undergo possible solidification that bring with it later defects or risks.


Probable mercury battery, which can be confused with the silver oxide battery. Source: Multicherry [CC0].

Mercury batteries are very characteristic due to their peculiar shape of silver buttons (image above). Most everyone would recognize them at first glance. They are also alkaline, but their cathode incorporates, in addition to graphite and manganese dioxide, mercury oxide, HgO; which, after being reduced, is transformed into metallic mercury:

Zn (s) + 2OH  (aq) → ZnO (s) + H 2 O (l) + 2e 

HgO (s) + H 2 O + 2e  → Hg (s) + 2OH 

Note how OH  anions are consumed and regenerated in these cell reactions .

Being small batteries, it is intended for small gadgets, such as watches, calculators, toy controls, etc. Anyone who has used any of these objects will have realized that it is not necessary to change the batteries for almost an “eternity”; which would be equivalent to 10 years, approximately.

Silver oxide

Silver oxide batteries. Source: Lukas A, CZE [Public domain].

The main defect of mercury batteries is that when they are discarded they represent a serious problem for the environment, due to the toxic characteristics of this metal. Perhaps this is why it lacks IEC and ANSI codes. For silver oxide batteries, their IEC code is preceded by the letter S.

One of the substitutes for mercury batteries corresponds to the silver oxide battery, much more expensive, but with less ecological impact (top image). They originally contained mercury to protect zinc from alkaline corrosion.

It is available with a voltage of 1.5V, and its applications are very similar to those of the mercury battery. In fact, at first glance both batteries look identical; although there may be much larger silver oxide piles.

The reactions at its electrodes are:

Zn (s) + 2OH  (aq) → Zn (OH) 2 (s) + 2 e 

Ag 2 O (s) + 2H + (aq) + 2e  → 2Ag (s) + H 2 O (l)

The water subsequently undergoes electrolysis, decomposing into H + and OH  ions .

Note that instead of mercury, metallic silver is formed on the cathode.

– Nickel-cadmium batteries (NiCad)

NiCd battery. Source: LordOider [CC0].

From this point the secondary cells or batteries are considered. Like mercury, nickel-cadmium batteries are harmful to the environment (for wildlife and health) because of the metal cadmium.

They are characterized by generating high electrical currents and can be recharged a large number of times. In fact, they can be recharged in total 2000 times, which is equal to extraordinary durability.

Its electrodes consist of nickel oxide hydroxide, NiO (OH), for the cathode, and metallic cadmium for the anode. The chemical rationale, in essence, remains the same: cadmium (instead of zinc) loses electrons, and cadmium NiO (OH) gains them.

The half-cell reactions are:

Cd (s) + 2OH  (aq) → Cd (OH) 2 (s) + 2e 

2NiO (OH) (s) + 2H 2 O (l) + 2e  → 2Ni (OH) 2 (s) + OH  (aq)

The OH  anions , again, come from the KOH electrolyte. NiCad batteries thus end up generating nickel and cadmium metal hydroxides.

They are used individually or coupled in packages (such as the one in yellow, image above). So they come in large or small packages. The little ones find use in toys; but the big ones are used for aircrafts and electric vehicles.

– Nickel-metal hydride (Ni-HM) batteries

Ni-HM batteries. Source: Ramesh NG from Flickr (

Another well-known cell or battery, and that exceeds NiCad in energy capacities, is that of Ni-HM (nickel and metal hydride). It can come in cylindrical format (conventional batteries, image above), or coupled in a battery.

Chemically, it has almost the same characteristics as NiCad batteries, with the main difference being its negative electrode: the cathode is not cadmium, but an intermetallic alloy of rare earths and transition metals.

This alloy is responsible for absorbing the hydrogen formed during charging, generating a complex metal hydride (hence the letter H in its name).

Although Ni-HM batteries provide more power (approximately 40% more), they are more expensive, wear out more quickly, and cannot be recharged the same number of times as NiCad batteries; that is, they have a shorter useful life. However, they lack the memory effect (loss of performance of batteries due to not being fully discharged).

It is for this reason that they should not be used in machinery that works long term; although this problem has been alleviated with LSD-NiHM batteries. Likewise, Ni-HM cells or batteries have very stable thermal characteristics, being operable in a wide range of temperatures without representing a risk.


The reactions that occur at your electrodes are:

Ni (OH) 2 (s) + OH  (aq) ⇌ NiO (OH) (s) + H 2 O (l) + e 

2 O (l) + M (s) + e   ⇌ OH  (aq) + MH (s)

– Lithium-ion batteries

Lithium-ion battery for a laptop. Source: Kristoferb from Wikipedia.

In lithium cells and batteries they are based on the migration of Li + ions , which are transferred from the anode to the cathode, a product of electrostatic repulsions due to the increasing positive charge.

Some can be recharged, such as laptop batteries (top image), and others, cylindrical and rectangular batteries (LiSO 2 , LiSOCl 2 or LiMnO 2 ) cannot.

Lithium-ion batteries are characterized by being very light and energetic, which allows them to be used in many electronic devices, such as smartphones and medical equipment. Likewise, they hardly suffer from the memory effect, their charge density exceeds that of NiCad and Ni-HM cells and batteries, and they take longer to discharge.

However, they are very sensitive to high temperatures, even exploding; and in addition, they tend to be more expensive compared to other batteries. Even so, lithium batteries are viewed favorably on the market, and many consumers rate them as the best.

– Lead acid batteries

Typical lead acid battery for automobiles. Source: Tntflash [CC BY-SA 3.0 (]

And finally, lead acid bacteria, as its name suggests, do not contain OH  but H + ions ; specifically, a concentrated solution of sulfuric acid. The voltaic cells are found inside their boxes (upper image), where three or six of them can be coupled in series, giving a 6 or 12 V battery, respectively.

It is capable of generating large amounts of electrical charge, and because they are very heavy, they are intended for applications or devices that cannot be transported manually; for example, cars, solar panels and submarines. This acid battery is the oldest and is still around in the automotive industry.

Its electrodes are made of lead: PbO 2 for the cathode, and spongy metallic lead for the anode. The reactions that occur in them are:

Pb (s) + HSO – 4 (aq) → PbSO 4 (s) + H + (aq) + 2e 

PbO 2 (s) + HSO – 4 (aq) + 3H + (aq) + 2e   → PbSO 4 (s) + 2H 2 O (l)

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