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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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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