As there is no « one cell fits all » solution, there isn’t any universal solution to connect a cell to a device. And that’s even truer when it comes to industrial applications. The way to connect the cell to your device depends on the size of the cell, the environmental conditions to which the device is going to be exposed, the need to replace the battery or not during the device’s life time, the volume to produce and whether it needs to be automatically or manually integrated on the printed circuit board (PCB), and of course, the cost of the equipment. It may seem trivial to some, but a wrong connection can result in inadequate, less effective devices.

In this article, we will give you some recommendations on how to choose the right connection; a solution that will last as long as your device is operating, without maintenance, thus helping you to maximize your end-users’ value and benefits.
 

The battery holder

The most popular system that we often find 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. It isn’t however 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 the cleaning is not performed periodically or during replacement.
• The system isn’t as sturdy as a rigid connections welded system or a wired connection. 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 the latter, we recommend two different solutions.  
 

Rigid connections welded system

For industrial applications, especially if the equipment is being fitted on large volume assembly lines for mass production, we recommend the usage of rigid connections electrically welded on the cell and then soldered on a Printed circuit boards (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 minimum connecting resistance. There is little chance of degradation during the device’s lifetime, it is economical, and it makes possible the automatic insertion of a cell on a PCB.

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

The soldered connections also have to 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, causing production line stoppages during assembly, or defective assemblies if the connections are not 100% precise. At Saft, we 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 2 or 3 leg connections on the positive and negative poles of our 1/2 AA , AA and A size Li-SOCl2 cells, in a precise and repeatable way, ensuring rapid, reliable and cost effective integration of the cells in the final device.  
 

Wiring connection with or without connector system

For bigger size cells such as C, D, or for 1/2AA, AA & A (Flying Lead finish above) when they are replaceable, there is a third possible way to connect the battery to the device: via a wire with or without a connector.

The wire’s length and the connectors’ types, from standard to specific ones, will need to be tailored to the device, a service that Saft can provide to its customers.

This solution offers a very good electrical connection as there is a minimum connecting resistance; it is very flexible which allows for a good fixation of the cell in the application even if the latter is submitted to shock and vibrations. You can place the cell further away from the PCB, the solution doesn’t degrade over time and makes it easy to mechanically polarize the slots or replace the cells if a connector is included.

However, if there isn’t a connector, no automatic insertion will be possible. You’ll need a visual polarizing slot. Changing the cell might also prove to be difficult as welding becomes necessary. Finally, the solution might come at a higher cost as it is personalized.

Thinking about the battery early in the design process is recommended as your choice of battery and battery connections will greatly impact your product design and cost of total ownership (CTO). Choosing the right connection for your device requires taking into account the whole life of the battery, from cradle to grave: during design phase, industrialization, serial life (logistics support), after sales, and disposal of the battery. Again, our application engineers will gladly advise you on how to optimize your electronic design. Don’t hesitate to get in touch!