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Battery Fundamentals

Chapter 26

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Objectives• Describe battery parts and operation• Understand how a battery converts chemical

energy to electrical energy• Explain battery capacity ratings• Select the correct battery type to use in a variety

of applications

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Introduction• Battery: heart of a vehicle's electrical system

– Converts electrical energy into chemical energy• Converts chemical energy back into electrical

energy

– Provides power to accessories

– Supplies current to the starter

– Acts like a capacitor

• Starter motor: largest load – Draws more than 100 amperes

– Battery voltage is low after use

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© 2012 Delmar, Cengage Learning© 2012 Delmar, Cengage Learning

Battery Parts and Operation• DC voltage

– Produced when two different metals are immersed in an electrolyte solution

• Automotive batteries– Plates provide 2.1 volts

– Fully charged positive plate: combination of lead and oxygen (i.e., lead dioxide)

• Plates: grids with horizontal and vertical bars

• Battery's case filled with electrolyte mixture

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Battery Parts and Operation (cont'd.)

• Battery cell – Consists of a packet of several positive and

negative plates

• Battery terminals – Connections are made of lead

– Some batteries have side terminals

• Battery case– Most are constructed of lightweight plastic

• Cell caps– Most battery tops have removable cell caps

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Battery Recharging and Discharging

• Current flows to battery from charging system– Battery explosions injure 15,000 people a year

• Battery discharging– Positive and negative plates become alike as the

battery discharges• Process is reversed during recharging

• After repeatedly charging and discharging– Active material on the cell plates is worn

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Battery Capacity Ratings• Battery capacity is related to:

– Surface of plates

– Weight of active materials on plates

– Strength of electrolyte solution

• Cold cranking amps (CCA) rating – Most common method of rating batteries

– Some manufacturers rate batteries in watt-hours

• Reserve capacity– Indicates how long a vehicle can be driven after

a charging system failure

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Battery Types• Batteries are designed for specific uses

– Deep-cycle: original battery design that was used in cars for many years

– Maintenance-free: have cell plates made of a slightly different material

– Low-maintenance: revision of the maintenance-free battery

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Battery Plate Size• Battery size is related to its reserve capacity

– Vehicles with larger engines and more accessories require batteries with more plate surface

• Recombination batteries – Sealed batteries using electrolyte gel or

microporous nonwoven glass

• Absorbed glass mat batteries – Do not use free-liquid or gel electrolyte

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Battery Selection• BCI lists group numbers

– Indicate physical size of batteries

• Considerations– Must fit the battery box

– Posts must be on the correct side of the battery

– Battery holddown must fit the battery

– Battery cannot be so high that it shorts on the hood

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Battery Service Life• Average battery

– Service life of three to five years

– Life is determined by amount of material shed from surface of positive plates

• Effects of sulfation– Usually reversible

• Effect of temperature on batteries– Batteries do not work well in cold weather

• Engine becomes harder to crank• Battery that is not fully charged will freeze easier

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Battery Cables• Must be large enough to carry all current

demanded by starter– Large cable is connected directly to the starter

– Cables for 12-volt systems are usually four or six gauge

• Battery terminal clamps– Made of plated steel, brass, or lead

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Battery Holddowns• Battery must be held

in its tray– Can fall out as the

car travels over bumps

– Excessive vibration can harm the battery

• Holddowns are made of steel or plastic

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Reasons for Battery Failure• Include:

– Damaged battery case can leak electrolyte

– Undercharging can cause sulfation

– Overcharging can cause buckled and warped plates

– Vibration can cause more material to be shed from plates

– Internal shorts between the plates can cause a dead cell

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Hybrid Electric Vehicle and Other Battery Types

• Other types of batteries include:– Nickel metal hydride batteries

• Subject to memory effect

– Lithium-ion batteries• Term used for all batteries that use lithium

• Typical hybrid battery – Most hybrid automobiles use NiMH batteries

• Paper membranes absorb electrolyte

• Hybrid battery pack gets hot– Has air cooling system

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© 2012 Delmar, Cengage Learning© 2012 Delmar, Cengage Learning