Guide: Batteries for Embedded Devices
With the many batteries available on the market, choosing batteries for embedded devices can be a daunting experience.
Today, we will put those doubts to rest. Learn all you need to know about batteries and how to choose a suitable one for your embedded device or product.
Brief Introduction to Batteries
Electric batteries are used to power electronics such as mobile phones, laptops and other mobile devices. Batteries contain cells with chemicals that undergo chemical reactions. In broad terms, these reactions result in a flow of electrons, which is the current that supplies power to our devices.
Batteries can be ‘primary’ or ‘secondary’. Primary batteries are designed for single-use only, whereas secondary batteries can be discharged and recharged multiple times by applying an electric current. Hence, secondary batteries are also known as rechargeable batteries.
Depending on what chemicals are used in the battery, they can be suitable for different uses. For example, alkaline batteries are widely used in consumer devices. Other types of batteries include lithium, zinc-air, or silver-oxide batteries.
Learn more about the underlying chemistry in batteries here.
Batteries in Embedded Devices
Battery power allows us to continue to use our embedded devices in situations where power lines are not readily available. In other cases, we may need our devices to be portable. For mobile electronic applications, the battery is critical in allowing our device to function properly.
Apart from having sufficient power, batteries form factors can be critical. Batteries they should also generally have good charge retention, providing a sufficient life span for an appropriate maintenance cycle (if at all).
Without further ado, let’s look at some considerations when choosing suitable batteries for our embedded devices!
Know the Specifications
Since battery chemistries are diverse and can be rather complex, we more commonly rely on battery specifications to choose our battery.
Battery Voltage
Battery voltage is measured in volts (V). It’s important to use a battery with the correct voltage rating for the embedded device that we are trying to power. Otherwise, it may malfunction or not work entirely – it may even be damaged.
The voltage rating by manufacturers is often a nominal measurement. The voltage of a battery at full charge usually starts at a higher voltage that quickly drops to its nominal value.
Then, it will gradually decrease over time until the voltage is low enough (referred to as the cut-off voltage) to consider the battery fully discharged or empty.
Cut-off Voltage
The cut-off voltage generally defines the empty state of the battery. This is because the voltage that can be supplied by the battery is no longer sufficient to power the devices that it has been rated for.
Battery Capacity
A battery’s capacity is a measure of how much energy it can store, usually expressed in Amp-hours (Ah). A battery’s Amp-hour capacity is calculated by taking the battery’s current (in Amperes or A), multiplied by the total amount of time for which this current can be supplied by the battery.
For example, mobile phone batteries with 4000 mAh capacity can supply the energy equivalent of 4000 milliAmperes of current for one hour.
Discharge Current
Although a battery may contain a given amount of energy, the current or rate at which it can be discharged or supplied to our devices safely is limited. The amount of current that can be drawn from a battery is measured in C. A higher C value means that more current can be drawn from the battery without causing damage.
Cycle Life
For rechargeable batteries, the cycle life defines how many discharge-charge cycles the battery can undergo before its performance deteriorates too far. Cycle life specifications are often estimated values as they are tested under standard conditions that may differ from our applications.
Recommended Charge Current
This is the ideal current that the battery should initially be charged at (to about 70%) before transitioning into constant voltage charging.
The charge current of a battery is especially important if we are considering renewable energy sources such as solar power. If there is insufficient solar energy to reach the recommended charge current, our battery may not be sufficiently charged for when it is needed.
Consider the Operating Environment
Simply selecting a sufficiently powerful or large battery is not enough. Keeping the operational environment in mind will not only improve the effectiveness of the product, but also its lifespan and safety for users.
1. Form Factor
It is important for our battery to be suitable in size and weight for our application. A battery for an electric vehicle, while large and powerful, is too big and heavy to use in a compact device such as a smartphone. This is especially true for mobile embedded systems, since they may need to fit into small compartments or even be wearable.
2. Operating Temperature
Batteries operate best at room temperature. At temperatures that are too cold or too hot, the capacity and performance of the battery will decrease.
Be sure to choose batteries which are rated to operate in the appropriate temperatures. For example, lithium iron phosphate batteries are more suitable for cold weather, capable of charging at low temperatures of -20 C (-4F).
Take note that temperature ranges for both charging and discharging have to be considered.
3. Dust, Humidity, and Others
Modern batteries can hold a great amount of chemical energy. As a result, they have reactive components that can be dangerous if exposed to the air. Consider specialised casings and seals for your battery to keep out dust, moisture and chemical ingress if your device is intended for use in a harsh environment.
Choosing the Battery
Now that we have covered the basic knowledge, it’s time to choose the batteries for our embedded devices. Ultimately, choosing a battery boils down to the following main questions:
- Primary or rechargeable?
- What is the required voltage, current, and capacity?
- What is the operating temperature?
- What form factor do you need?
- How much maintenance can be afforded?
- Do you need a special enclosure for your battery?
Here are some of the popular battery choices:
Non-Rechargeable Batteries
| Type | Advantages | Disadvantages | Uses |
| Alkaline Batteries | Small size, Efficient, Low Leakage | High cost | Torches, remotes, small appliances |
| Coin Cell Batteries | Light, high density, low cost, high nominal voltage | Needs a holder, Low current draw capability | Watches, clocks, miniature electronic products |
Common Secondary Batteries
| Type | Lead Acid | NiCd | NiMH | Li-Ion* |
| Cell Voltage | 2V | 1.2V | 1.2V | 3.2-3.6V |
| Discharge Cutoff Voltage | 1.75V | 1.00V | 1.00V | 2.50V |
| Discharge Current | 5C | 20C | 5C | 2C or >30C |
| Cycle Life | 200-300 | 1000 | 300-500 | 500-1000 |
| Self-Discharge / month | 5% | 20% | 30% | <5% |
| Charge Temperature | -20 to 50 oC | 0 to 45 oC | 0 to 45 oC | 0 to 45 oC |
| Discharge Temperature | -20 to 50 oC | -20 to 65 oC | -20 to 65 oC | -20 to 60 oC |
| Maintenance Requirement | 3-6 months | Full discharge every 90 days when in full use | Full discharge every 90 days when in full use | Not required |
| Cost | Low | Moderate | Moderate | High |
For general use, you might find that Li-ion batteries are the most suitable due to no maintenance, high cycle life and low self-discharge. This is why they are popular in many appliances such as laptops and mobile phones. One disadvantage, however, is cost.
For more information on different types of batteries and their advantages, please visit:
Tips to Maintain Your Battery
While battery performance naturally deteriorates over time and with use, proper maintenance and care can go a long way to protect the batteries in our embedded devices.
- Where possible, always operate batteries at room temperature
- Charge and discharge batteries slowly. Side reactions occur more rapidly at higher rates, hurting battery capacity and lifespan.
- In general, do not fully discharge a battery unless otherwise recommended. A full discharge can alter the battery chemistry irreversibly.
- Study and understand the requirements of the chosen battery. For example, some Nickel-based batteries do need to be fully discharged occasionally.
- Lower your depth of discharge (DOD). Simply put, a lower discharge between charging cycles can vastly improve the battery’s cycle life.
Some Batteries and Tools to Get Started
Here are some of our recommendations to get you started! For best results, always refer to the product specifications on each of their pages.
Note: As Li-ion / Li-Po batteries will generally be sufficient for small electronics, we have placed greater focus on their recommendation in this section. For more batteries, kindly visit our battery catalog.
General Purpose Battery – Battery Kit – 3.7V 520mAh
This battery kit includes a battery and a battery indicator board. The battery indicator board features 4 LEDs to conveniently indicate the charge-level of the battery. It also carries the standard JST-1.0 and JST-2.0 connectors, in case you want to use it with another battery.
Renewable Recharging Capabilities – Solar Panels and Cloths
Solar solutions are an environmentally friendly solution for powering our embedded devices. Since there is no need to recharge and little maintenance requirement, solar panels or cloths can be used for devices that need to last for long durations in remote locations.
However, take note that solar power relies heavily on available sunlight, and does not offer large discharge currents compared to the typical battery. For critical operations, it is recommended to pair solar power with a battery for emergencies.
Smart Battery Solution – LiPo Rider Pro
The LiPo Rider Pro is the perfect accessory for your embedded device if you want to supplement battery power with solar power. Featuring two standard JST-2.0 connectors and an LED indicator, the on board integrated circuit will even handle power flow to your device from each of the sources conveniently. It can even be used to charge the battery with solar power. Just plug and play!
Proprietary Batteries (Wio Terminal, Seeduino Xiao Batteries)
Some devices have proprietary batteries or battery accessories specifically developed for them. In that case, we highly recommend going with them since they will definitely be compatible with your device. For example, here are our recommendations for the Wio Terminal and the Seeeduino XIAO.
- Wio Terminal – Wio Terminal Chassis Battery 650mAh
- Seeeduino Xiao – Grove Shield for Seeeduino XIAO – with embedded battery management chip
- Seeeduino Xiao – Seeeduino XIAO Expansion Board
Conclusion
Congratulations! You’re now equipped with sufficient knowledge to choose batteries for your mobile embedded devices.
Although the process to find our perfect battery can be daunting and sometimes frustrating, remember that a battery is what enables a mobile product to be the best that it can be!
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