As more systems go mobile, batteries are becoming increasingly integral to design. They come in all shapes, sizes, and capabilities but no single one is perfect for all challenges.
Lead-Acid
The lead-acid* battery has been around since 1859 and is the most common rechargeable battery solution. As the legacy staple battery, Lead-acid batteries are typically available at 12V or 6V with 2V per cell and various capacities to accommodate a lot of uses—from small motorbikes to cars, and even enormous battery banks that help maintain cell phone towers through power loss.
Advantages
One of the primary advantages of the lead-acid battery is high power density which is unique from energy density. When a device has high power density it means it can sustain high current draws for a period of time. This high current carrying capability has made lead-acid batteries very common in vehicles to support the cranking of an engine which can demand as high as 650A for a large 8 cylinder diesel engine. Another factor that gives an edge to the tried-and-true lead-acid battery is its wide temperature range functionality. A lead-acid pack can generally handle higher and lower temperatures than competing chemistries and still function well.
Lead-acid batteries are also commonly used for backup power systems, including for telephone and computer centers, grid energy storage solutions and uninterruptible power systems (UPS). Such systems increasingly are adding Internet connectivity and becoming part of the IoT. For instance, UPS systems are linking to the Internet to report data for performance monitoring. This allows UPS systems to communicate their status remotely to signal when they need maintenance or perhaps when they have been activated during a power outage.
Downsides
A lead-acid battery can do great things when in the right applications but it does have significant trade-offs. While the power density is high, the energy density is low, meaning that compared to other portable power systems, it will take up more space and weigh more. For an application like a Smartwatch it would be impractical to attach a giant lead-weight battery, but for a vehicle the extra weight may not be as much of an issue.
A lead-acid battery is the one to use when your system is not weight or space constrained but needs lots of current carrying capability and a durable battery power source. Essentially, the lead-acid battery is at the bottom end of the scale for energy density but is the well-known, “old-reliable” battery solution that has simply lost popularity in today’s lightweight and portable world.
Alkaline
When everyone hears the word “battery”, they almost immediately think of something like AA or AAA alkaline batteries. Although you can now find almost all battery chemistries in those form factors, alkaline* batteries are almost exclusively found in the form factors that we associate with household batteries. As a general rule of thumb, an AA alkaline battery can deliver 700 mA of current at a general voltage of around 1.5 V, which is why they are so commonly found in household handheld electronics. Alkaline batteries have a higher energy density that nickel-metal hydride batteries and have been higher than some rechargeable Lithium-ion batteries.
Downsides
One of the main downsides to alkaline batteries is that they are very susceptible for leaking what people commonly call “battery juice” or, more acutely, potassium hydroxide. This is a result of the battery discharge, whether through usage or gradual self-discharge. When an alkaline battery discharges, hydrogen gas is created which causes an internal pressure within the battery. This pressure can eventually lead to a rupturing of the battery wall, thus leaking potassium hydroxide. Potassium hydroxide reacts with CO2 to form the toxic and irritating crystalline potassium carbonate which is what we all know as the gross white stuff on the side of old batteries. The more you know! Alkaline batteries were also historically made with mercury until 1996, which means that they were a pain to dispose of.
Alkaline batteries have been seen in applications ranging from CD players and TV remotes to Tickle-Me Elmo’s. And just about any other child’s toy in the last 30 years, for that matter. For higher current demands, such as large flashlights and stereos, you can also find larger form-factor alkaline batteries such as C and D cell batteries.
Nickel-Metal Hydride/Nickel-Cadmium
Next on the scale of energy density come the nickel-metal hydride* and nickel-cadmium batteries. NiMH and NiCD batteries both occupy a similar spot in terms of capabilities but NiCD cells have been getting replaced quickly by NiMH because NiCD cells have been outlawed within the European Union, except for specific uses, due to their toxic nature. NiMH batteries also possess a better energy density, about 30-40% higher, than NiCD but are generally less resistant to overcharge. NiMH batteries are less susceptible to memory issues but also have a higher self-discharge rate—which means they have a shorter storage life before needing a recharge. Both chemistries generally allow around 1.2V per cell and have good current handling capability.
In systems that have space and weight concerns but that still need decent current output, you can achieve an affordable solution using NiMH cells. The primary driver for using NiMH over something like lithium-ion would be cost and possibly cycle life, but both of these factors are being reduced with newer battery technology. While Li-ion batteries are taking market share in most portable electronics products, NiMH may see some usage in Internet-connected consumer devices in the future.
Advantages
Some of the greater advantages of Ni-Cd batteries are that they are offered at a lower cost compared to some alternative rechargeable technologies. Ni-Cd is also more durable and able to work better under rough conditions, including low temperatures. With the capability to deliver high surge currents, Ni-Cd batteries are well suited for use in remote-controlled applications. Because of that, Ni-Cds are finding usage in drones, which now are joining the IoT.
With a higher energy density over lead-acid and alkaline batteries, NiCD and NiMH also found a lot of uses in portable systems and especially in portable power tools that require decent current output. While Li-ion batteries are taking market share in these products, NiMH may see some usage in Internet-connected consumer devices in the future.
Singing the Praises of Lithium-Ion
Ah, finally! What you have been waiting for.
Since Sony Corp. released the first commercial, rechargeable Li-ion* battery in 1991, the technology has gained rapid acceptance as an energy storage technology. The term lithium-ion can be a bit deceiving, since it encompasses a wide range of chemistries that are not all equal but that all feature a lithium based anode and a cathode of another material. Lots of work has been done to optimize the materials in these cells for various uses and you should look into their tradeoffs before settling on a specific cell. The typical cell voltage is between 3.6V and 3.8V, but they have a limited ability to handle high currents.
Advantages
One major advantage of Li-ion batteries is their high volumetric energy density, meaning the amount of electricity they can store in a given space. The volumetric energy density of Li-ion batteries is up to 620 watt-hours per liter (W-h/l). This is more than four times the density of nickel cadmium (NiCD) batteries, an alternative rechargeable battery technology, which has a maximum of 150 W-h/l. This high density is one of the features of Li-ion that makes it desirable for space-constrained products, such as mobile phones.
Li-ion batteries also have limited susceptibility to the memory effect that plagues other rechargeable battery types. The memory effect describes the tendency of certain batteries to lose their capacity for charge after they are repeatedly recharged and not fully discharged. Because of these attributes, Li-ion has gained acceptance in applications where long life and low maintenance are key. These are critical factors behind Tesla’s use of Li-ion in its electric cars and its Powerwall solar energy storage system. Furthermore, Li-ion batteries are undergoing technological improvements, with the use of new materials and structures, increasing their capacity and reducing recharging times.
Recent changes in construction and chemistry have lead to significant improvements in the general capacity of lithium-ion cells. These high rated cells are becoming popular in airborne systems such as multi-rotor vehicles. At the moment, for most portable systems, I would recommend lithium based solutions as they will be lighter and more compact giving you design flexibility, although this will generally be more expensive than a comparable NiMH or lead-acid solution.
Downsides
Li-ion technology is not perfect, and comes with some drawbacks. Most notably, Li-ion costs more than alternative batteries, at 40 percent more than nickel-cadmium (Ni-Cd), according to one estimate. Li-ion also is subject to aging, reducing the amount of charge the battery can hold over time. One lithium-ion option, however, is the CR2032 coin battery, which uses lithium/manganese dioxide (Li/MnO2). Commonly used in electronic watches, this type of battery is useful in small devices that need a long charge.
One other note about lithium based solutions: They have a nasty habit of not handling stress very well when charging or discharging. If a lithium cell becomes stressed and is not properly protected it can cause a fire or even an explosion of the type that was recently on display in the Boeing 787 Dreamliner. To address this issue in lithium cells, more design work is still needed for protection than you would see in lead-acid or NiMH batteries. To learn more about the dangers of Lithium Ion batteries, click to READ MORE.
A Battery of Batteries
Lithium-based batteries are the most commonly used batteries in modern technology, with lithium-ion’s (Li-ion) use in marquee products like Tesla’s Powerwall and Apple’s iPad/iPhone. However, Li-ion batteries and their variants may not always be the best choice for every application or every IoT device. A number of alternative battery chemistries are available that may be more suitable depending on the way they will be used.
For high-volume applications that have low-power usage, such as certain wearables, alkaline batteries may be sufficient. Alkaline batteries are inexpensive and available from a wide variety of suppliers in standard sizes, from tiny CR1216 devices used in electronic watches to giant D-cells. For other devices that can be maintained by users, including heart and blood pressure monitoring systems, standard-sized batteries are sufficient, including AA and AAA varieties. Some other systems require rechargeable batteries. Beyond Li-ion, other common rechargeable battery types include Ni-Cd, nickel-metal hydride, (NiMH) and lead acid.
To learn more about safety concerns of different battery chemistries, click to READ MORE
*To search for specific battery chemistry (ex. Lithium, NiMH, alkaline), use the parametric search bar on the battery page, navigate to the Chemistry category and search or scroll to select the desired battery chemistry.
