---
categories:
  - Electronics
tags: [physics, electricity]
---

# Cells and batteries

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

> The key thing to remember: **cells configured in series increases the overall voltage available** and **cells configured in parallel increases the overall current available**

### 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, it is not accumulative. We represent this as follows:

$$
I_{T} = I_{1} + I_{2} + I_{3}
$$

However the voltage is accumulative: it is the _sum_ of the individual cell voltages, represented below as [electrical field](/Electronics/Physics_of_electricity/Voltage.md#distinguishing-voltage-from-electric-field):

$$
E_{T} = E_{1} + E_{2} + E_{3} \\
$$

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In the case of **series opposing**, negative terminals are connected to each other and positive terminals are connected to each other in a series. This doesn't have many applications.

### Parallel connections

Parallel connections follow the series opposing (negative to negative, positive to positive) configuration but they are not connected in sequence.

_The same current flows through all cells. This is represented mathematically as follows ($T$ stands for time)_: