Choosing the right battery for your smart device is not an easy task and depends on many parameters. 

Not only does the battery need to be light and small-sized to fit into miniaturized designs, but also remain safe all over a long-life expectancy (thanks to good charge retention). Another crucial point for the battery is to be able to operate in a wide range of temperatures (for both indoor and outdoor usages) while offering a stable output voltage throughout the device’s lifetime.

Before going any further into which parameters to look at, let’s get back to basics: What are the various batteries available to us and what are their specificities? 

What are the various batteries available to IoT entrepreneurs and what are their specificities?

There are two types of batteries: primary batteries that are single-use and secondary batteries that are rechargeable. 

Both generate electricity through electrochemical reactions between two poles, positive (+) and negative (-), and thanks to an electrolyte (solution). Using various materials for the poles and different electrolyte compositions, we can make a huge variety of batteries with different properties and voltages. For example, alkaline batteries are widely found in shops and used in consumer products, lithium batteries, zinc-air batteries, silver-oxide batteries or a mix of these chemistries are examples of batteries available on the market. 

Wireless connected objects require light and compact batteries with very high energy density and high voltage. For that reason, lithium batteries are best suited.

Indeed, lithium batteries offer high performance and reliability, feature high voltage thanks to the use of lithium as anode, and deliver an amount of energy per volume that can be ten times more than that of zinc-oxide batteries. Its electrolyte contains no water, allowing for use at low temperatures, and some products with specific electrolytes can sustain high and even very high temperatures. 

Lithium batteries come in various forms and sizes. 

Saft's lithium batteries dedicated to the Internet of Things

The result of more than one hundred years of research and innovation in the field of energy storage, our range of miniature lithium-based batteries has been specially designed for connected object (IoT) applications. 

We offer 3 main ranges of batteries for IoT devices:

• LS, LSH and LSP cylindrical primary lithium cells & batteries
• LM/M cylindrical primary lithium cells
• Medium prismatic MP and cylindrical small VL rechargeable cells
   

LS, LSH and LSP cylindrical primary lithium cells – 3.6 V

Saft’s LS, LSH and LSP cylindrical primary lithium cells ranges are based on Lithium-Thionyl chloride (Li-SOCl2) chemistry, which exhibits the highest nominal voltage among primary battery chemistries (3.6 V). 

LS, LSH and LSP batteries have also the highest energy density and can restore it for up to 20 years. They are very sturdy and can withstand very high temperatures and strong vibrations.

Two types of lithium thionyl chloride cells are available: bobbin and spiral constructions. 

The bobbin construction of the LS range makes these cells particularly well suited for applications requiring very low continuous or moderate pulsed currents such as metering devices or parking sensor applications. 

Their ability to withstand broad fluctuations of pressure, temperature (from - 60°C to + 150°C) and harsh mechanical environments make the LS cells ideal for use in remote locations and extreme environments such as trackers. Combined with a pulse support such as a capacitor, super capacitor, EDLC (Electrochemical Double Layer Capacitor) or Hybrid capacitor, they can even sustain higher pulses and temperatures and combine “best of both worlds” performances. 

That's why Saft’s launched a new range of primary solutions –the LSP– that combines reliable, low self-discharge Li-SOCl2 cell technology in parallel with a state-of-the art and carefully selected LiC (Lithium-ion Capacitor).

The LiC selected by Saft is showing the lowest self-discharge and ESR (Equivalent Series Resistance) at most temperatures and one of the highest measured capacitance during a pulse, ensuring that the LSP range will meet the lifetime of 10 years or more required by the new generation of connected devices. In a nutshell, the LSP range offers the best compromise between pulse sustaining capability, operating temperature range, and performance stability over lifetime.  

The LSH range has a spiral construction. The cells are designed for applications requiring very high pulses. Some specific ranges can operate at the very high temperatures found in oil and gas applications, for example. 

LM/M cylindrical primary lithium cells – 3 V

The Saft LM/M cylindrical primary lithium cells are based on lithium-manganese dioxide (Li-MnO2) chemistry – 3V.

LM/M cells have a spiral internal construction like LSH cells but exhibit a lower nominal voltage of 3.0 V vs. 3.6 V. If the electronic design of the application is allowing a cut-off voltage below 2.5 V, this range is probably one of the most economic options with a good trade-off between energy and power. LM/M range features high surface-area spiral electrodes for maximum current pulse capability and an electrolyte formulation for optimized operation from - 40°C to + 85°C.

Their good pulse capability makes them suitable for smart metering devices requiring high pulses, but also parking sensors and smart farming applications.
 

Medium prismatic MP and cylindrical small VL rechargeable cells - 3.6 V - 3.75 V

Saft medium prismatic MP and cylindrical small VL rechargeable cells are based on our unique lithium-ion technology. These batteries can be recharged and used again and again after discharge which makes them very convenient for devices that are frequently used. Saft MP and VL batteries boast very long cycle-life in harsh conditions, as they can be charged and discharged over a wide temperature range. Our lithium-ion batteries are equipped with specific safety features – electronic protection circuit, a built-in circuit breaker in case of a charger fault, shut-down separator, and safety vent - which makes them more expensive than most other batteries, but high cycle count (up to 2 800 times with only a 30% capacity loss) and low maintenance reduce the cost per cycle over many other chemistries. In addition, state-of-charge (SOC) and state-of-health (SOH) indicators may be selected as options to monitor your application. Saft’s Li-ion technologies offer unique performances in unregulated outdoor conditions or in extreme conditions, either hot or cold. They are therefore ideal for demanding applications in industrial and critical environments. 

Below is a table of our battery ranges and the applications they can be used for: 

So… Long story short! Which battery for my IoT application? 

As you will have understood by now, there is no simple answer to that question. 

Here are the parameters you must consider when listing all the options for your use case:

• The nominal and cut-off voltage of your electronics: there are different technologies and chemistries having different output voltages. You should pick the one that will ensure your device to be above the cut-off voltage throughout its lifetime. 
• The environment’s temperature: You should think about where your IoT device will be deployed to ensure an optimal and continuous supply power to your object. 
• The consumption’s profile and the maximum pulse current and frequency: Li-SOCl₂ bobbin technology is more relevant to use for limited pulse values and for a long lifetime, whereas Li-SOCl₂ spiral, Li-SOCl₂ bobbin + pulse support device and Li-MnO₂ are particularly suited for high pulse applications. 

Still confused about how to move forward with your choice? Why don’t you submit your use case’s consumption profile to our application engineers for a personalized recommendation?