Low-power design: what it means for battery selection

“Low power” has been a longstanding mantra for IoT developers, further accelerated by the advent of low-power wide area (LPWA) technologies such as LTE-M or NB-IoT.

Low-power design aims to reduce the overall dynamic and static power consumption of a device for the purpose of optimizing battery lifetime.

It goes well beyond simply inserting a mobile operator’s NB-IoT SIM card into a device.

It requires engineering and optimizing of every part of a device’s hardware and software. The connection time should be limited and, depending on the wireless technology chosen, many parameters require finetuning to optimize device performance and power consumption. A sleep mode also needs to be incorporated to keep power consumption to a minimum during intervals of no communication.

As a result, designing for low power places presents challenges around connectivity, power consumption and robustness. For the batteries that power these applications, there are several considerations and trade-offs between performance, energy, and power consumption that can make the selection process tricky.

Let’s delve deeper into low-power design and what it means for choosing the right battery.

Three key considerations for low-power design

Communication behavior is one of the biggest drivers of IoT battery life, with factors such as communication frequency, payload size, protocol choice and firmware updates all affecting energy consumption.

Smaller payloads and efficient transmission schedules reduce retransmissions and lower power use, and devices are placed in low-power sleep mode whenever possible, since unnecessary communications interrupt power-saving functions in NB-IoT and LTE-M systems.

Selecting and configuring connectivity correctly is equally important. Poor handling of network failures can cause repeated device reboots and reconnections, draining batteries and potentially congesting networks.

Tools such as radio policy management can help detect these situations and apply back-off mechanisms to limit unnecessary activity. For mobile deployments, restricting network scans to required operators and frequency bands can also shorten acquisition time and reduce energy use.

Hardware selection and configuration strongly influences device power consumption.

Multimode communication modules can improve coverage flexibility but generally consume more energy than single-mode alternatives due to their more complex architectures. GNSS (Global Navigation Satellite System) receivers must also be configured carefully, as satellite positioning can become a major power drain.

Other hardware choices have a knock-on effect on a device’s ability to be truly ‘low-power’. Inefficient power components dissipate energy as heat, while poor antenna placement can reduce performance in LPWA frequency bands, undermining coverage and battery efficiency.

Battery life can be extended by processing data locally rather than sending raw information to the cloud. Edge computing enables devices or gateways to analyse data on-site, reducing bandwidth, latency and communication energy, and embedded AI can further inform smart decisions about when communication is necessary.

However, overall power consumption must be considered carefully. Reduced communication often offsets additional processing demand, but continuous sensing and computation can eliminate these gains. The balance between computing and transmission should therefore be evaluated across the full power budget.

Choosing the right battery for low-power design

Battery selection should be addressed at a very early stage of a project.

Different chemistries offer different benefits and can be adapted to a device’s consumption profile.

Lithium-Thionyl chloride (Li-SOCl2), for example, is an interesting chemistry for low-power, long-life applications as it offers a low selfdischarge (meaning that that the battery’s capacity doesn’t get too impacted by storage time and use in sleep mode) and perfectly suits high-energy and high-voltage requirements in a wide range of temperatures.

This chemistry is subject to passivation, a surface reaction that protects the cell from discharging on its own and enables its long shelf life.

However, the power requirements need to be anticipated to find the right trade-off between the consumption profile and the energy load.

The passivation layer will build during sleep mode or in storage, before breaking to let the current through when needed. But, if the main energy consumption current is too low, ions from peak communication current won’t be able to flow through the passivation layer, causing the voltage to drop below the cut off voltage and the device to stop. So, understanding passivation pitfalls (and how to avoid them) is a really good place to start when choosing the correct battery.

The construction of the cell is also important, as it has a direct impact on the performance of the cell.

Bobbin cells provide higher energy density and lower self-discharge than spirally designed cells but the limited current and pulse current capability, which is often required in LPWA applications, might require the use of a pulse sustaining device, such as a capacitor, EDLC or Hybrid Layer Capacitor, to achieve higher pulse currents profiles. Saft’s LS/LSH/LSP range covers each of these potential construction choices.

There are additional considerations for designers to make.

Field temperature can play a major role in battery performance. In fact, for the same IoT application, different deployment environments may call for different battery chemistries. As mentioned earlier, in hotter climates Lithium-Thionyl Chloride batteries can experience increased passivation that can reduce usable cell capacity. In those cases, Lithium-Manganese Dioxide may be a better fit because it is not affected by passivation in the same way.

Choosing between battery technologies often comes down to finding the right balance of voltage, current capability, and system design. There are several ways to optimize that balance. A high-voltage chemistry like Lithium-Thionyl Chloride can be paired with a supercapacitor to support stronger current pulses. Lithium-Manganese Dioxide, which naturally handles pulse demands well, can be combined with a DC/DC converter when additional voltage is needed. Designers can also boost voltage by using battery packs or connecting cells in series.

In general, higher operating voltage tends to improve electronic efficiency. Since battery power is determined by both voltage and current, lowering a device’s operating voltage typically increases the current draw required from the battery and, over time, that higher current demand can shorten battery life.

So, there’s a lot to think about when choosing a battery for low-power design. There’s no ‘one size fits all’ approach, and investing time early in the process can help developers to understand their application’s profile, identify the right battery, and avoid costly redesigns.

Fortunately, Saft has a range of smart tools that can help.

The Saft Smart Selector can steer developers towards optimal battery technologies based on key parameters. Book Your Technical Deep-Dive offers developers the chance to draw on Saft’s expertise with one-to-one contextual guidance that can aid the design process.

And, for later in the development phase when the electronic design is finalized, the Online PSR creates a structured dialogue around the application’s detailed energy profile and gives Saft’s application engineers exactly what they need to confirm the required battery solution and get an accurate lifetime estimation – meaning developers can confidently take the next step of industrializing their low-power product.