1.2V Battery

An electric battery is essentially a source of DC electrical energy. It converts stored chemical energy into electrical energy through an electrochemical process. This then provides a source of electromotive force to enable currents to flow in electric and electronic circuits. A typical battery consists of one or more voltaic cells. 

The voltage of electric batteries is determined by:

• Chemistry. The potential difference of the materials that compose the positive and negative electrodes in the electrochemical reaction.
• Number of cells. Batteries in series produce a voltage equal to the number of batteries multiplied by the voltage of each individual battery.

It doesn’t matter what format the battery is. For example, an AA battery has the same voltage as an AAA battery.

The voltage of electric batteries is created by the potential difference of the materials that compose the positive and negative electrodes in the electrochemical reaction. Because most of the resulting voltages are around 2V, cells are connected in series to obtain more practical electrical potentials (i.e. six 2V lead acid cells are connected in series to obtain a typical 12V battery).

1.2V – NiMH Battery

A nickel metal hydride battery, NiMH, is a rechargeable battery with a positive electrode made of nickel hydroxide and a negative electrode made of a metal hydride (a hydrogen-absorbing alloy). The NiMH battery was commercially introduced in 1989 and was mainly used as a power source in portable personal computers. Since then, the NiMH battery system has become very popular in electric hybrid vehicles and makes up 10% of the total market for rechargeable batteries. Compared to the NiCd battery, the NiMH provides 40 percent higher specific energy resulting in about two times higher capacity. NiMH batteries are also less affected by voltage depression, but the main advantage is the absence of toxic cadmium. The memory effect of NiMH batteries is much less than nickel-cadmium batteries.

The overall reaction during discharge is:

NiO(OH) + MH → Ni(OH)₂ +  M

During this process, free electrons are bound so that this pole becomes the positive electrode. The redox voltage of the reduction is approximately 0.49 V. The total voltage of the redox reaction is thus E⁰ = 0.49V – ( – 0.83V) = 1.32V.

1.2V – Nickel-cadmium Battery

The nickel-cadmium battery (Ni-Cd battery) is a type of secondary battery using nickel oxide hydroxide Ni(O)(OH) as a cathode and metallic cadmium as an anode. The abbreviation Ni-Cd is derived from the chemical symbols of nickel (Ni) and cadmium (Cd).

The battery has low internal impedance resulting in high power capabilities but lower energy storage capacity compared to other battery systems. It has long cycle life and the capability of rapid recharge but may suffer from voltage depression or memory effect, meaning that the maximum charge voltage will decrease and hence the energy capacity if continuously discharged shallowly. The greatest disadvantage is the content of cadmium. Unfortunately, cadmium is extremely toxic; therefore, the Ni-Cd will not be an alternative for a modern battery system.

The overall reaction during discharge is:

2NiOOH + Cd + 2H₂O → 2Ni(OH)₂ +  Cd(OH)₂

Cell Voltage

The voltage of electric batteries is created by the potential difference of the materials that compose the positive and negative electrodes in the electrochemical reaction. 

The voltage produced by each lithium-ion cell is about 3.6 volts. This has many advantages. Being higher than that of the standard nickel-cadmium, nickel metal hydride, and even standard alkaline cells at around 1.5 volts and lead acid at around 2 volts per cell, the voltage of each lithium-ion cell is higher, requiring fewer cells in many battery applications.

Because most of the resulting voltages are around 2V, cells are connected in series to obtain more practical electrical potentials (i.e. 2V lead acid cells are connected in series to obtain a typical 12V battery).

Batteries with voltages greater than 1.5 volts are usually made up of cells connected in series inside a single case. In the 9 volt battery, there are six cells connected in series. The calculation is 6 × 1.5 Volt = 9 Volt.

To know the voltage of a battery, batteries are marked with nominal voltages which is the average voltage a cell outputs when is fully charged, but this may differ from the open circuit voltage.

In addition, some factors like low temperature can decrease the expected voltage output and increase with higher temperature, which is favorable for the electrochemical reactions.

To avoid batteries to discharge below a certain level which could cause damaging the battery, there is a voltage limit called cut-off voltage.

• 1.5V (DC) – A common open circuit voltage for non-rechargeable alkaline batteries (e.g. AAA, AA and C cells). 
• 3V (DC) – Lithium-based primary cells are batteries that have metallic lithium as an anode. The voltage of most lithium-metal cells (e.g. button cells) is 3V.
• 3.8V (DC) – Almost all lithium-ion batteries work at 3.8 volts. In order to make current flow from the charger to the battery, there must be a potential difference. Therefore battery chargers or USBs for almost all smartphones provide a voltage of 5V.
• 12V (DC) – A common voltage for automobile batteries is 12 volts (DC). But this battery consists of six 2V lead cells.

Why are alkaline batteries (AAA or AA) made to be 1.5V while rechargeables are 1.2V?

In general, batteries convert stored chemical energy into electrical energy through an electrochemical process. This then provides a source of electromotive force to enable currents to flow in electric and electronic circuits.

• Primary (single-use or alkaline) batteries use cells that have 1.5V open circuit voltage when fresh. 
• Secondary (rechargeable) batteries use cells from NiMh or NiCd, which have 1.2V open circuit voltage.

In practice, alkaline batteries and rechargeable batteries can be used interchangeably in sets. They have only different voltage characteristics. It is given by their different chemistry. Primary cells gradually drop in voltage from use. They start at 1.5 volts, drop to 1.2 and continue to 1.0 where the appliance stops working. Secondary cells operate more uniformly, even with only 1.2 volts. They have flat discharge where they pretty much stay at 1.2 volts until depleted and then drop off very quickly to below 1.0 volts.

Since electronic devices are usually made to run from cell voltages of 1.0 to 1.5 volts, alkaline batteries and rechargeable batteries perform similarly. In fact, it’s generally considered that secondary 1.2 V cells work better than alkalines having lower output impedance and more consistent voltage from start to finish of a charge.

Other Types of Batteries

The following list summarizes notable electric battery types composed of one or more electrochemical cells. Four lists are provided in the table. The first list is a battery classification by size and format. Then, the primary (non-rechargeable) and secondary (rechargeable) cell lists are lists of battery chemistry. The third list is a list of battery applications. The final list is a list of different battery voltages.