Battery Pack Connections

Series and Parallel connections

Various applications operate at different voltage levels and require different levels of electrical power to run; there are many different cells around today with different voltages, capacities, electrical characteristics, chemistries and physical dimensions. Even with such a range of different cells avilable, certain devices require different levels of electrical power and the only way to deliver this is by making a larger battery out of a number of cells connected together.

This section outlines how cells can be connected together to produce a battery with the required voltage and capacity. Initially the electrical characteristics of the various connections are discussed, then details of limitations and various safety issues that need to be taken into account when connecting cells together.

For these examples, let us assume we are using Alkaline cells with a voltage of 1.5v each with a capacitance of 2700mAh.

Serial connection

With series connection, the total voltage of the pack will be the sum of the individual cell voltages. The overall capacitance of the cells remain the same, so for the configuration above:

Total Voltage = 1.5 + 1.5 = 3v

Total Capacitance = 2700mAh

Parallel connection

With parallel connection, the total voltage will remain the same as that of an individual cell. It is the capacitance which changes, increasing with each battery added to the arrangement so that the total capacitance of the pack becomes the sum of the individual cell capacities:

Total Voltage = 1.5v

Total Capacitance = 2700 + 2700 = 5400mAh
= 5.4Ah

Combined Series/Parallel connections

It is common, especially when the power requirements of a device become relatively large. There are many ways to connect a group of batteries in both series and parallel within the same pack. This increases the range of voltage and capacity characteristics that can be provided by such packs. There are many different ways in which these connections can be made; how this is done will not only depend on the power requirements of the device, but also the space requirements of the application.

Because of this, there are numerous ways in which batteries can be arranged; not only the connections between the batteries can vary, the way in which the batteries are arranged can also vary. For details on common pack configurations see the Battery Pack Configurations section.

Important battery pack information

1. You cannot solder directly to a battery, if you wish to connect cells together or fit a connector to them they must have solder tags on them, soldering directly to a cell the heat can cause it to explode.
2. Only batteries of the same size, chemistry, manufacturer and age should be conected together to form a battery pack. Using cells that do not match each other can cause imbalance within the pack causing the pack not to function correctly, damage the applications or cause a risk of fire or explosion.
3. Only primary non rechargeable cells can be connected in parallel to increase the capacity of the pack. Due to the nature of charging battery packs, rechargeable cells cannot be connected in paralell unless specific conrrcuitry is incorporated into the pack. Because of this, the only way to increase the capacity of a rechargeable battery pack is to use larger cells to make the pack.
4. When constructing large primary non-rechargeable packs which use parallel strings to increast the capacity, protection must be cosidered in order to ensure the strings across the pack discharge evenly. Uneven discharge can cause parallel strings with higher remaining capacity to discharge into the other strings causing damage to the pack and the possibility of fire, explosion or leakage.
5. With any battery pack protection devices may need to be considered to safeguard the pack against damage through short circuit, high drain currents, reverse connection, temperature or overcharging depending on the type of pack.

If you have any queries regarding pack design please don't hesitate to contact a member of our team by using the contact details below.