What’s the best way to integrate a battery into your device?

There is no simple way to answer that. Just as there is no ‘one cell fits all’ solution to selecting the right battery, there is no universal solution to how you go about connecting a cell to a device

That’s even more true when it comes to industrial applications. The best means of connecting the cell to your device depends on a number of considerations:

• the size of the cell
• the environmental conditions to which the device is going to be exposed
• whether the battery will need replacing during the device’s lifetime
• the volume of devices being produced
• whether it needs to be automatically or manually integrated on the printed circuit board (PCB)
• the cost of the equipment

Getting the connection wrong can result in inadequate, less effective devices. So in this article we explore the different connector systems to help you choose the right connection for your device.

The battery holder

The most common system found in consumer applications is the battery holder. Easy to use and generally inexpensive, it offers the advantage of letting the end user replace the cell easily. However, it isn’t adapted to industrial applications for several reasons:

• The risk of mixing different cell technologies or different cell state of charge is more important, especially if the replacement is being performed by an inexperienced user.
• The cell could be positioned the wrong way (inversion), which could lead to safety issues.
• The system is not adapted for long-life applications as there is a risk of micro-corrosion of the terminals if cleaning is not performed periodically or during replacement.
• The system isn’t as sturdy as a rigid connections welded system or a wired connection (see below). The battery holder could lead to a risk of micro-cut of voltage in case of shock or vibrations during transport or usage.

If this technology is adapted for consumer products using alkaline cells, it is not recommended for industrial applications using Saft products. For our batteries, we recommend two more suitable solutions.

Rigid connections welded system

For industrial applications, especially where the equipment is to be fitted on large volume assembly lines for mass production, we recommend the usage of rigid connections electrically welded on the cell, and then soldered onto a PCB on the other side. Different kinds of connections exist to allow this assembly with or without a polarizing slot:

This technology is particularly well adapted for small size cells (AA & A). It offers a perfect electrical connection with a minimal connecting resistance. There is little chance of degradation during the device’s lifetime, it is economical, and it makes the automatic insertion of a cell on a PCB possible.

However, because it creates a rigid link between the cell and the PCB, the mechanical fixation of the cell creates constraints if the application is subject to shock and vibrations. This limits the usage of welded systems for C and D size cells. Additionally, cell replacement isn’t easy due to the welding.

The soldered connections must be very precise, especially for automated mass production. The dimensional tolerances of the cells, particularly at the level of the soldered connections, can be slender. This can cause production line stoppages during assembly, or defective assemblies if the connections are not 100% precise.

Saft have created an automatic connection installation with a level of precision that is unmatched on the market in terms of process repeatability. The machine is used to laser weld two- or three-leg connections on the positive and negative poles of 1/2 AA , AA and A size Li-SOCl2 cells, in a precise and repeatable way. This ensures rapid, reliable and cost-effective integration of the cells in the final device.

Wiring connection with or without connector system

For larger cells such as C, D, or for 1/2AA, AA & A (using the Flying Lead (FL) finish per the above image) there is a third possible way to connect the battery to the device, if they are when they are replaceable - via a wire with or without a connector. The wire’s length and the connector type, from standard to specific, need to be tailored to the device - a service that Saft can provide to its customers.

This solution offers an excellent electrical connection as there is a minimum connecting resistance, and it is very flexible which allows for a solid fixation of the cell in the application even if the latter is submitted to shock and vibrations. Furthermore, a wiring connection allows you to place the cell further away from the PCB and the solution doesn’t degrade over time.

If a connector is included, the system also makes it easy to mechanically polarize the slots or replace the cells. However, if there isn’t a connector, no automatic insertion will be possible, and you will need a visual polarizing slot. Changing the cell might also prove difficult as welding becomes necessary

This solution might be more costly because it is more tailored your device – but that may be a long-term cost saving to your end user as it provides a reliable, effective connection.

The right solution for you

Finding the right connection for your application often comes down to planning. Commit time in the early design process to consider the right battery, and then the right battery connection, as it will help with your product design and cost of total ownership (CTO). Choosing the right connection for your device means taking into account the whole lifespan of the battery - during design phase, industrialization, serial life (logistics support), after sales, and disposal of the battery.

*This is an updated version of an article first published in October 2020.