Cells are a [voltage source](/Electronics/Physics_of_electricity/Voltage.md#chemicals-cells-and-batteries) that generate a difference of potential via a positive and negative electrode separated by an electrolytic solution. The electrolytes pull free electrons from one of the materials which creates a positive charge. The other material gains the free electrons creating a negative charge.
> A battery is a combination of two or more cells.
> Cells which cannot be recharged are called **primary cells**. Cells which can be recharged are called **secondary cells**.
## Connecting batteries
Cells and batteries can be connected to each other in electrical ciruits to increase the overall voltage that is produced. There are three main connection types:
- series
- parallel
- series-parallel
### Series connections
With series connections we distinguish **series aiding** and **series opposing** configurations.
In the case of series aiding, cells are connected one in front of another with the positive terminal connecting to the negative terminal of the other in a line.
In this configuration the **same current flows through all the cells**. This is represented mathematically as follows ($T$ stands for time):
$$
I_{T} = I_{1} + I_{2} + I_{3} \\
$$
The voltage is the sum of the individual cell voltages (represented here as [electrical field](/Electronics/Physics_of_electricity/Voltage.md#distinguishing-voltage-from-electric-field)).
