How to Select the Optimal Battery Technology for Your Application

A close up of electronics Description automatically generated
Published on by John Teel

Choosing a battery for a given application involves more than just knowing the application requirements. An understanding of the underlying technology of each battery type, its characteristics, limitations, and advantages, is required in order to select the right type of battery.

The batteries described here are all based on electrochemical processes that produce electricity. We’ll be looking at both disposable and rechargeable battery technologies.

NOTE: This is a long, very detailed article so here's a free PDF version of it for easy reading and future reference.

 

Table 1 below shows the most important factors to consider when choosing a particular battery type for a given application.

FactorsConsiderations
Full charge voltage and end of charge voltageThese determine the minimum number of cells to use for a given application. Alternatively, it may dictate the use of voltage converters or regulators.
CapacityHas to be consistent with the expected run time of the application.
Maximum rate of dischargeAlso known as specific power density. All cells have limits on the maximum current they can safely provide. If this doesn’t meet the application requirements, consideration should be given to increasing the number of cells in the battery pack, or choosing cells with higher discharge rates.
Temperature rangeAll cells have capacity changes with temperature. They have other temperature dependencies too.
Size and weightThe energy density per unit volume (volumetric), and per unit weight (gravimetric), of various cell technologies should be considered.
SafetySome types of cells need additional protection, electrical and mechanical, in order to operate safely.
Self-dischargeAll cells self-discharge even when not used – some more than others.
DegradationThis applies mostly to rechargeable cells. Their capacities permanently degrade with the number of charge/discharge cycles.
Shipping requirementsThis one is not so evident. Some battery types have stringent shipping requirements, specifically for air-shipments.
RecyclingSome countries require that the equipment manufacturer provide a way to recycle their used batteries.

Table 1 – General considerations for including batteries in any application

 
Before going further, note that a battery pack is defined as being made up of one or more such cells bundled together into a single unit. Sometimes additional circuitry is included for protection, fuel gauging, or temperature sensing.

Disposable Batteries

These types of batteries are non-rechargeable, and are discarded after use. They typically come in well-defined standard sizes such as AA, AAA, C, D and various coin types.

The next sections briefly describe the technologies and uses of the major types of disposable batteries.

Alkaline, zinc-carbon, and lithium batteries

These can be easily found everywhere. They are available as cylindrical or button types, and 6V or 9V types. The typical open-circuit voltage of a fresh single cell is nominally 1.5V, but can be as high as 1.65V. The end of discharge voltage is around 0.9 – 1.0V.
 

A picture containing indoor, sitting Description automatically generatedFigure 1 – Standard size alkaline batteries

 
Alkaline cells have between 3 – 5 times the gravimetric energy density of zinc-carbon batteries with around 100 to 190 Whr/Kg (watt hours per kilogram), depending on the discharge rate. Whereas non-rechargeable lithium batteries have around 200 – 270 Whr/Kg.

Since the available sizes are standard, these figures can be used to roughly estimate the weight of the battery needed for a given application.

They are capable of moderate discharge rates at the expense of reduced capacities. For example, AA batteries can be discharged at 800 mA to 1.0A at room temperature – less in fully enclosed spaces.

Coin-type batteries

These are mostly zinc-air or silver oxide chemistries which have nominal voltages of about 1.3V – 1.6V, and lithium manganese dioxide types at about 3.0V.

Except for lithium manganese, these batteries have very low discharge current capabilities.
 

A close up of a device Description automatically generatedFigure 2 – Various coin-type batteries

 
On the other hand, a lithium manganese coin cell such as a CR2032 can be discharged at 100mA or more, and at low discharge rates it has a very flat discharge curve.

So, unless the extra cost is a consideration, lithium manganese is usually recommended for applications requiring coin cells.

Special types

If the application requires a battery that has a shelf life of 15 – 20 years, has high energy density, and can operate from -55°C to greater than 85°C, then a lithium thionyl chloride battery should be considered.

The main drawback is that it is only capable of a very low discharge rate. This means a large decoupling capacitor is usually required to improve its transient response. Lithium thionyl chloride batteries are also expensive.

Rechargeable batteries

There is a wide range of choices for rechargeable batteries. Due to that, there is an equally wide set of issues to consider when selecting the proper technology to match the application.

Lead Acid

Lead acid batteries have low gravimetric and low volumetric energy densities, respectively at around 34 – 40 Whr/Kg and 60 – 75 Whr/L. Thus, for a given amount of energy storage, they are very large and heavy.

Their cell voltage is around 2.1V, however, they are usually available as 6V or 12V batteries. Self-discharge is high at 5 – 20%/month. What distinguishes them is their very high discharge rate capability and their relatively low cost. Also, charging them can be very simple.

Lead acid batteries are most commonly used in automobiles. They are almost never used in consumer electronics.

NiCad batteries

NiCad batteries have been mostly supplanted by other types with better cost-performance ratios. However, they are still widely in use at this time so it’s good to understand their pros and cons.

NiCad batteries are not recommended for use in new designs. See table 2 below for some of their main characteristics.
 

PropertyValueNotes
Nominal voltage1.2 VCannot replace alkaline batteries in some cases due to this lower value.
Energy densities40-60 Whr/Kg and 50 – 150 Whr/LNot as high as other rechargeable batteries.
Specific power density~ 150W/KgThey can provide large sustained current and even larger bursts.
Self-discharge~ 10%/monthModerately high, and varies with temperature.
Cycle life1500 – 2000 cyclesUseful life will be quite long. Due to a memory effect, they permanently lose capacity if consistently recharged from a specific discharge point. It is recommended to occasionally fully discharge the battery, and then fully recharge it.
OtherSome countries, mostly European, have placed severe restrictions on the use of NiCad batteries.

Table 2 – Characteristics of NiCad batteries

 

Nickel Metal Hydride (NiMH) batteries

NiMH batteries have replaced NiCads in most applications where they would have been considered before.

Two things to watch out for are cycle life, which is quite low, and self-discharge, which is quite high.
 

A close up of a book Description automatically generatedFigure 3 – Rechargeable NiMH batteries

 
There are some low, self-discharge types on the market, but they typically have lower energy densities. Also, charging them requires specific, though widely available, chargers.

Table 3 shows some of the major characteristics of NiMH batteries.
 

PropertyValueNotes
Nominal voltage1.2 VCannot replace alkaline batteries in some cases due to this lower value.
Energy densities60-120 Whr/Kg and 140 – 300 Whr/LModerately high for commonly available rechargeable batteries.
Specific power density>250W/KgThey can provide large sustained current and even larger bursts.
Self-discharge15% – 80%/monthVery high. There are special low self-discharge types.
Cycle life~ 300 – 350 cyclesPermanent capacity loss can be severe after this number of cycles, making them quickly unusable, especially at moderately high discharge current.

Table 3 – Characteristics of NiMH batteries

 

Li-ion batteries

Li-ion batteries actually fall into many sub-types even though, at a fundamental level, they store energy in similar ways. This is, by far, the technology with the highest energy density and the widest selection.

Li-ion batteries are also by far the most common battery technology used to power modern electronic products. They mainly come in three different form factors as shown in figure 4 below.
 

Figure 4 – General form factors of li-ion cells

 
The cylindrical and prismatic types have rigid, pre-formed metal cases.

The pouch type, known somewhat incorrectly as lithium-ion polymer or LiPo, has a casing made up of laminated nylon, aluminum and polyester materials.

This type offers the most shape flexibility since they are easily customizable. Some suppliers will even do custom shapes for moderate production volumes.

Figure 5 shows some examples of curved or irregular-shaped pouch-type batteries.
 

A close up of a knife Description automatically generatedFigure 5 – Curved and irregular-shaped custom LiPo batteries.

 
Yet another type, known as solid-state batteries, can be made into extremely thin and flexible, but offer low capacity.
 

A close up of a device Description automatically generatedFigure 6 – Example of a solid state battery

 
The flip side of li-ion technology, however, is they require stringent precautionary measures in order to provide safe operation and handling.

Pay particular attention to safety when using lithium-ion batteries, otherwise you may find your product catching on fire like happened with the Samsung Galaxy Note 7 back in 2016/2017.

Mechanical considerations

Lithium-ion batteries have to be securely mounted inside the enclosure. If the battery can rattle around when the device is jerked or dropped, and it gets dented or bruised, internal shorts in the core can occur. These, in turn, can cause overheating, or even explosions.

In addition, lithium-ion cells will swell as they age and the battery compartment has to accommodate this increase in size. Again, this can also cause bruising of the core.

Electrical considerations

The li-ion cell must have a Protection Circuit Module (PCM), usually bundled together to make it into a battery pack. The PCM must provide Under-Voltage Protection (UVP), Over-Voltage Protection (OVP), and Over-Current Protection (OCP).

Li-ion cells do not take well to being over discharged. They will suffer permanent damage. They also cannot be charged much beyond their maximum charge voltage. Even 0.5V of overcharge is too much, and they will run a risk of thermal runaway.

Finally, they have to be protected against over-current discharge, or else they will overheat, and swell up.

This all seems very complicated, but, fortunately, there are chips that integrate all these components. Most battery vendors provide packs that already include the PCM. I always recommend that you only use lithium-ion batteries that have the PCM built-in so as to reduce your chance of an accident during early testing, and to decrease your own liability.

On top of the PCM, li-ion batteries have strict multi-stage charging requirements that include pre-charging, full rate charging and taper charging.

They also have both low and high temperature limits on when charging is allowed. Specifically, li-ion batteries should not be charged at low temperatures – below 0°C to 10°C, depending on the manufacturer.

Doing so repeatedly will cause lithium plating – a very dangerous condition that can cause the battery to catastrophically fail, sometimes hours after charging, when the battery is just sitting idle.

PCM’s have a temperature sensor, usually a Negative Temperature Coefficient (NTC) thermistor. This provides temperature readings to the charger controller that, in turn, disables charging beyond the safe limits.

Again, there are various chips that can handle this task with various cost/performance tradeoffs. The system itself should also shut down if the battery temperature gets too high during use.

Regulatory approvals

Because of all of the above, li-ion batteries have to be certified before they can be used in most commercial products. For the North American market, the cells have to be UL1642 certified. The battery packs should be IEC62133 certified.

In addition, to be able to ship the cells by air, they should be UN38.3 certified. Also, note that they fall under the Dangerous Goods Regulations of IATA.

This requires, among other things, that batteries shipped in bulk meet certain state of charge requirements, as well as packaging and labeling requirements. Li-ion batteries cannot be shipped in bulk on passenger aircrafts.

Common types of li-ion batteries

Almost all common types of li-ion batteries use graphite, or graphite with some percentage of silicon or silicon oxide as their anode, or negative electrode.

The positive electrode, on the other hand, can be one of several material types, from which the type names are derived. Common cathode materials include Lithium Manganese Oxide (LMO), Lithium Cobalt Oxide (LC), Lithium Iron Phosphate (LFP), and Lithium Nickel Manganese Cobalt Oxide (NMC).

They each offer various tradeoffs among nominal voltage, energy density, maximum charge and discharge rates, specific power, and cycle life.

Table 4 provides these key figures for the various types. In this table, the C-rate is defined as the actual stored energy of the battery, in Whr (watt-hours), divided by the nominal voltage.

To get the Whr of a battery from the energy density given in Wh/Kg, simply divide it by the weight of the battery. A 200 Whr/kg, 1 kg, battery has a stored energy of 200 Whr. If its nominal voltage is 20V, then the C-rate is 10A.
 

ParameterLMOLCONMCLFP
Nominal Voltage (V)3.73.7 – 3.853.7 -3.853.2 – 3.3
Energy density (Whr/Kg)100 – 150200 – 220200- 220100 – 120
Max. Charge rate (C)1C1C1C1C
Max. Discharge rate (C)1C – 2C1C – 2C1C – 2C1C – 20C
Cycle life (20% degradation)~500~500800 – 10001000 – 2000

Table 4 – Characteristics of common li-ion battery types

 

Conclusion

The choices of battery types can be a bit overwhelming at times. However, the large majority of products will use either disposable alkaline batteries, disposable lithium coin cell batteries, or rechargeable lithium-ion batteries.

Only in rare cases will any of the other battery technologies be used.

Although the large majority of new products use rechargeable lithium-ion batteries you need to be aware of the extra complications these batteries create.

From a technical standard most of the complications due to lithium-ion batteries are taken care of by the built-in PCM, and the wide availability of easy to use battery charger chips.

However, they do add extra product cost, and require several additional levels of certification.

In some cases disposable alkaline batteries make the most sense, at least initially. Perhaps their use could be one way to simplify your Minimum Viable Product (MVP). Later you have the option to release a version with a rechargeable lithium-ion battery.

The key to success is knowledge of the obstacles that lie in your path and a realistic plan on how to overcome those obstacles. Helping you accomplish this is the goal of the Predictable Hardware Report.

If you need affordable coaching, training, and support to help bring your new electronic hardware product to market then be sure to check out the Hardware Academy program.

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Gregg LevineTjade RubenJohn TeelLarry Nelson SrKari Recent comment authors
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Gregg Levine
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Gregg Levine

First things first. Good article. Second things second, I needed to go to your blog here, because on Medium it did not show the selected photos. And next, they never did explain why that particular cell phone self destructed like that ahead of schedule.

Tjade Ruben
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Tjade Ruben

Hi John. Thanks for sharing this information with us. There is one time of battery you didn’t consider “Fuel Cell”.
I don’t know if there are promising for the future of aircraft technology.

Larry Nelson Sr
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If Watt hours is 200 and nominal voltage is 20 then by your definition the C rate is 10A and not 2A.

John Teel
Admin

Good catch Larry, thanks for pointing this out. I have fixed this error.

Kari
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Kari

Is there a mixup with Lithium Manganese and Lithium Thiolyn chloride battery discharge properties?

John Teel
Admin

Hi Kari,

No I don’t believe so. The main characteristics of lithium thionyl chloride batteries are low self-discharge rates, wide operating temperature range – much wider than lithium manganese cells. However, their internal impedance is high; thus, they have low discharge rates.

Thanks for the comment.

Gregg Levine
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Gregg Levine

That’s partially why that style of lithium batteries are used in military gear requiring primary only. I believe they were also developed about the time we started to explore the outer planets in greater detail as well.


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