How to Select a Non-Rechargeable Battery Pack

Batteries are not all created equally. There are several different types of batteries, rechargeable (or reusable), non-rechargeable (single use) and reserve batteries. Reserve batteries are a special class of non-rechargeable batteries that endure extremely long storage; greater than 20 years&#; shelf-life.

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EaglePicher® Technologies manufactures more different types of electrochemistries, rechargeable and non-rechargeable batteries, than any other company in the world. This intimate knowledge of batteries allows EaglePicher to be chemistry agnostic and supply the best cell chemistry for a given market.

Take Performance Into Account

In addition to different electrochemistries, the internal cell design and the external cell format attributes can have a significant impact on performance, most notable energy and power. Generally, a cell will be either an energy design or a power design, but not both.

In order to properly compare cell chemistries, performance must take into consideration both capacity and voltage. Therefore, it is best to compare watt hours. This is illustrated by the standard measurements of specific energy (Wh/kg) and energy density (Wh/L), both of which are expressed in watt hours. Another measure of performance that is used is power or watts. If power is the most critical parameter then the best approach is to contact EaglePicher&#;s design experts for help in battery selection.

In most cases, the power source (cell or battery) is a critical component of any device; therefore, evaluating the tradeoffs in terms of performance as part of the preliminary evaluation is advantageous. The first step in selecting the best battery for a given application is to determine which type of battery is the most appropriate &#; rechargeable, non-rechargeable or reserve.

For reference, cell chemistry or electrochemistry are the active chemical components in a cell that stores the chemical energy such as lithium or carbon monofluoride. A cell is a single unit that stores the chemical energy, a battery is a collection of one or more cells with external connections. Cells and batteries store the chemical energy and allows for the conversion of chemical energy into electrical energy.

Pros and Cons of Different Battery Attributes

A brief synopsis of the positive and negative attributes of the batteries are given below:

Reserve Batteries:

Reserve batteries are a unique subgroup of non-rechargeable batteries. Their most important attribute is shelf-life. A reserve battery can deliver full capacity after over 20 years of storage. No other battery can deliver this performance after decades. If long shelf-life (>10 years) is part of the specification a reserve battery should be selected. EaglePicher is the world leader in the design and production of reserve batteries. Therefore, if it is determined that a reserve battery is most appropriate for your application contact EaglePicher&#;s battery design experts.

Non-Rechargeable versus Rechargeable Batteries:

Even though a non-rechargeable battery cannot be reused there are attributes which will lead to the selection of a non-rechargeable cell chemistry. Some of the differences between non-rechargeable and rechargeable batteries are:

• Cost: Because a non-rechargeable battery is used once and discarded, but normally has 2 to 3 times the energy density as rechargeable, its cost can be as much as 2 to 3 times greater than a rechargeable battery.
• Convenience: For the most part, non-rechargeable batteries are ready to use as delivered and can be used in remote locations (military, fire-fighting, etc.) where recharging equipment is not available or practical. In contrast, rechargeable batteries are not shipped at 100 percent state of charge (SOC), less than 30 percent SOC by law and therefore have to be recharged prior to use.
• Self-discharge rate: Self-discharge occurs naturally due to chemical reactions; however, non-rechargeable batteries have a far lower self-discharge rate than rechargeable batteries due to the differences in electrochemistries. A load that draws current only periodically will usually run for a longer time period with a non-rechargeable battery than loads powered by rechargeable batteries, which lose their charge over time.
• Shelf-life: For rechargeable batteries, shelf-life is more complicated than simply self-discharge. This is a result of having two components of self-discharge for rechargeable cells, reversible and irreversible. If stored incorrectly, a rechargeable cell will lose capacity permanently. The best method to store rechargeable cells varies according to cell chemistry. Additionally, some rechargeable batteries require periodic SOC monitoring and provisions for recharging to ensure their long-term health and readiness for use.
• Specific Energy (Wh/kg): Non-rechargeable batteries provide greater energy on a weight basis than rechargeable batteries, up to a factor of four times.
• Energy Density (Wh/L): Non-rechargeable batteries also provide greater energy than rechargeable batteries on a volumetric basis; however, this advantage is less than on a weight basis.
• Power Density: Generally, non-rechargeable batteries have a higher internal resistance than rechargeable batteries, which relates to the rechargeable battery&#;s higher self-discharge rates. There are, however, non-rechargeable reserve batteries that are equivalent or better in power density than rechargeables.

Energy Requirements

Design engineers usually work from a document, supplied by the user, with specifications to meet the device mission requirements. The nominal battery life is often specified, which leads the designer to consider basic issues of battery capacity, energy density, power density and usage profiles.

The fundamental measure of capacity is the ampere hour (Ah), a measure of the battery's stored electrochemical energy. A battery rated at 1Ah and 1 ampere (A) rate capability for instance, will send a constant current through a load that draws 1A for one hour before reaching end of discharge (EOD). However, there's more to consider.

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The internal resistance of the battery provided by the manufacturer, is a measurement at beginning of life. Generally, the internal resistance increases as the battery is depleted and effectively limits a battery's output capacity. Battery capacities are determined under a set of conditions that must include discharge rate and temperature. As the rate of discharge increases or the temperature decreases the delivered capacity will also decrease. Delivered capacity is dependent on applied load, operating temperature and cut-off voltage. For instance, a battery rated at 2Ah continuously delivering, say, 0.400A, may not reach its EOD for five hours (2Ah/0.4A = 5 hours). But, when the load demands 1A continuously, the battery will reach its EOD in less than two hours. The internal resistance of the battery consumes some of its capacity naturally, which manifests as voltage drop and heat.

Therefore, for devices or specifications that are driven by power requirements it is best to choose a battery with the lowest possible internal electrical resistance. The overall ampere hour capacity is far less important than the internal cell construction that allows for large current draws without excessive heat generation.

Battery Chemistry

When designing a battery, there will be trade-offs. Battery chemistry determines many of the final product's characteristics while internal battery design (the materials and components) also has an influence. The internal design of the cells can also be optimized for high energy (capacity) or power (rate), or tailored to provide a medium ratio of both. Therefore, cell design can be used to improve rate capability of a specific cell chemistry. However, each individual electrochemistry will have inherent rate capability limitations due to kinetic influences of the cathode and anode, distinct from cell design. Another attribute of the cell chemistry which cannot be changed is voltage. This is due to the electrochemical couple of the two electrodes and the differences in electromotive force between the two electrodes; increasing battery voltage, for a specific chemistry, is achieved by configuring multiple cells in series.

Lithium Batteries

Lithium batteries have dominated the high performance non-rechargeable battery market over the last 40 years. This is due to lithium anodes having the following attributes:

• High voltage: Greater than 3.0V compared to 1.5V for commercial alkaline cells. With a higher voltage the number of cells in a battery will be reduced by a factor of two. This due to the relative placement of lithium in the electrochemical series, high electro-positivity.
• High epecific energy and energy density: The energy delivered by a lithium battery is two to five times greater than other non-rechargeable battery systems.
• • Lowest molecular weight of a metal, 3,862 mAh/g for lithium metal.
  • Good rate capability &#; some lithium cell designs, non-rechargeable and rechargeable can be discharged rapidly.

Lithium Batteries &#; Non-Rechargeable Chemistries

Not to be confused with lithium-ion rechargeable batteries, these are disposable batteries that use lithium metal for the anode. In addition to the positive attributes listed above for all lithium batteries, non-rechargeable lithium batteries have the additional performance characteristics:

Wide operating temperature - lithium batteries can perform between -40°C and +70°C; some lithium batteries work at >165°C, or as low as -80°C.

Flat discharge curve - constant voltage over most of the discharge life of the battery is common for lithium non-rechargeable cells/batteries.

Excellent shelf life - lithium batteries can be stored for several years, 10 years at room temperature or longer under lower temperatures. This is far better performance than all non-rechargeable battery systems.

For all non-rechargeable lithium batteries, the anode is lithium metal. Therefore, the differentiator is the cathode material, and to a lesser extent, the electrolyte which vary across a range of chemistries. Several lithium battery systems manufactured by EaglePicher are listed below.

• Lithium Carbon Monofluoride (Li-CFx):
  The most common EaglePicher Li/CFx cell is a 3.0V primary D cell designed for military and other applications where a lightweight cell that will operate safely over a wide temperature range is needed. With a capacity of 16Ah and specific energy of 471 Wh/kg, an energy density of 838 Wh/L, this chemistry can deliver up to 10A for 20 seconds when needed. This cell is designed for high energy at moderate rates (<1A). This cell chemistry operates between -40°C and 165°C.
• Lithium Carbon Monofluoride/Manganese Dioxide Hybrid (Li/CFx-MnO2):
  The Li/CFx-MnO2 cell chemistry was developed to overcome some of the deficiencies of the Li/CFx system to enable discharge at higher rates such as 2A continuous. At 2A and 20°C the individual D cell will deliver 15.5Ah and 402 Wh/kg and 743 Wh/L. This cell chemistry operates between -40°C and 70°C.
• Lithium Thionyl Chloride (Li/SOCl2):
  Power cells or battery packs are ideal for applications where a small current flow is needed intermittently for as long as 10 to 15 years. Li/SOCl2 chemistry, provides a high energy density compared to other lithium designs, typically 450-700 Wh/kg and 850-1,200 Wh/L, packed into exceedingly small packages. Li/SOCl2 cells have an open circuit voltage of 3.67V and a nominal operating voltage up to 3.6V. With an extended operating range, these batteries are suitable for both extremely low and extremely high temperature environments, generally, from -40°C to more than 95°C, with some operating at temperatures as high as 165°C.
• Lithium Oxyhalide (Li/SOxCl2):
  These high energy batteries have a voltage of 3.95V and are custom-built, largely for military applications where a one-time burst of power is required for about 5 to 20 minutes. These batteries can be stored for more than 20 years and can deliver 250 Wh/kg, even at temperatures below -32°C

Contact EaglePicher Technologies For Other Battery Considerations

Manufacturers provide additional information on temperature ranges suited for each battery type and whether a battery pack is restricted or requires special handling under Class 9 Dangerous Goods Shipping Guidelines.

For expert advice on these and other non-rechargeable battery packs &#; including silver-zinc, thermal batteries and others &#; refer contactto EaglePicher Technologies to learn more. EaglePicher has served aerospace, defense and aviation markets since when EaglePicher introduced the first special purpose battery. Our batteries are a key component of the U.S. space program, including powering the International Space Station, Mars Rovers, commercial jets and helicopters and more than 85 percent of U.S. missile platforms.

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