Spring 2009 Forward to a Friend

Battery Illustration
Batteries - What's Inside?

EVERY SUBARU HAS A BATTERY UNDER THE HOOD – THAT BLACK, RECTANGULAR, RUBBERY-LOOKING BOX THAT HAS TWO GRAY POSTS STICKING UP WITH CABLES ON THEM. WE TEND TO THINK ABOUT BATTERIES ONLY WHEN THEY “DIE.” WHAT DO THEY DO? WHY ARE THEY IMPORTANT?

Factors that shorten battery life:

  • Remaining in discharged state for a long period
  • Deep discharging and charging cycles
  • Dirt and acid buildup
  • Inadequate charging
  • Overcharging
  • Vibration and movement
  • Physical damage
  • Extremely hot or cold temperatures
  • Loose or corroded terminal connections

A vehicle’s battery is a critical workhorse: It converts chemical energy into electrical energy, which turns the engine’s starter and operates ignition systems and other electrical components. If the battery doesn’t work, nothing else does.

A battery provides the potential for electrons to flow. Making a connection between a battery and a starting motor causes energy conversion. Electricity turns the starter, which starts the engine. After the engine starts, its alternator provides the electrical current needed by the vehicle’s electrical system and recharges the battery.

BATTERY CELL CONSTRUCTION

Within a vehicle’s lead-acid battery case are cells filled with electrolyte.

Each cell has plates made of active materials contained in cast grids. Plate grids are flat, rectangular, lattice-like castings.

Positive plates contain lead dioxide. Negative plates contain sponge lead dioxide.

In each cell, positive and negative plates alternate.

To ensure plates don’t touch, separators are inserted between them. Separators are made of nonconduction material. They are chemically resistant to sulfuric acid, strong, and yet porous enough to allow electrolyte passage. They prevent active chemicals from touching each other.

The assembly of plates and separators is called an element. There is one element per cell.

Each cell produces approximately two volts. Battery cells are connected in series to produce different voltages. A vehicle requires 12 volts, or six two-volt cells.

ACTIVE BATTERY PROCESS

A battery is activated by the addition of electrolyte, which is a mixture of sulfuric acid and water. The electrolyte causes chemical action between lead dioxide of a positive plate and sponge lead of a negative plate. The electrolyte moves electrical current between positive and negative plates through the separators.

As the current flows, the battery becomes discharged. During discharge, lead peroxide, sulfuric acid, and water separate. Sulfur combines with negative-plate sponge lead and positive-plate lead; the remaining oxygen combines with hydrogen.

During charging, chemical and electrical actions are reversed by the engine’s alternator.

TYPES OF BATTERIES

Older vehicles typically have conventional batteries that require the periodic addition of water to keep plates covered with electrolytes.

Today, batteries are maintenance-free, which means they shouldn’t require added water. Some have a built-in water-level indicator or visual test indicator in the cover. Maintenance-free batteries have envelope separators and expanded grid plates that contain calcium, cadmium, or strontium to reduce gassing and self-discharge. They also have better overcharge resistance and less of a tendency toward terminal corrosion than conventional batteries.

MAINTENANCE

It is important to have batteries tested to help identify their performance levels. Subaru original-equipment batteries are covered by the Subaru New Car Limited Warranty for three years/36,000 miles. Subaru replacement batteries come with an 85-month limited warranty when installed by an authorized Subaru dealer, and a 30-month/unlimited-mileage free replacement with free towing to the nearest Subaru dealer if the vehicle is inoperable due to battery defect.


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BATTERY MAINTENANCE

All Subaru vehicles are equipped with maintenance-free batteries. The term “maintenance-free” can be deceptive – these batteries require some attention to maintain their cleanliness and efficiency.

The battery is the heart of the electrical system and the main cause of winter weather start-up woes.

Cold weather effects:

  • Batteries lose about half their strength
  • Increased demands on batteries
  • Reduced engine-cranking power
  • Thickened engine oil, which makes engine turnover difficult
  • Cold fuel, which doesn’t vaporize well
  • Reduced battery recharging efficiency

It is extremely important to have your car’s battery checked regularly by a Subaru-trained technician. Technicians look for:

  • Loose or corroded connections that can dramatically diminish your car’s starting power
  • Loose (or crusty) connections that can shut off your car’s electrical flow entirely (imitating a dead battery)

Winter driving frequently requires the use of lights, defrosters, and wipers for extended periods. This requires the charging system to work properly so it functions adequately. For this reason, your service technician should check your battery’s charging system and voltage regulator and inspect your alternator to ensure components are operating properly.



According to the Subaru Owner’s Manual, it is unnecessary to periodically check battery fluid level or periodically refill with distilled water. However, if the battery fluid level is below the lower level, remove the cap. Fill with distilled water to the upper level.