What Causes a Dead Cell in a Car Battery?

Written by jared beck
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What Causes a Dead Cell in a Car Battery?
Check your car battery's voltage regularly to avoid dead cells. (battery charger image by Albert Lozano from Fotolia.com)

Basic car batteries are composed of six cells, each filled with an electrolyte solution of sulphuric acid and water. Sometimes these cells become deficient and lead to complete battery failure.

Cell Anatomy

Plates of lead and lead dioxide are submerged in each cell's electrolyte solution. In a fully-functioning battery, each cell provides 2.1 volts of electricity, totalling 12.6 volts for the battery. These cells are called "wet cells."

Battery Function

The cells are connected in series and, when the ignition is turned, a chemical reaction occurs between the plates and the sulphuric acid, turning the lead into lead sulphate. This also creates an electrical current, known as discharging the battery. The current then transfers to the alternator and starts the engine. When the car is off, the battery recharges: the lead sulphate slowly releases the sulphur and reforms as lead.

Electrolyte Leakage

Dead cells may occur if electrolyte solution leaks out, causing an inadequate amount of solution to safely discharge the battery. In this case, the cell will not produce its 2.1 volts and the other cells will have to work harder to produce the 12.6 volts necessary to start the car. Over time, one weak cell can cripple other cells and cause cell failure.

Shorted Cells

Cells may short-circuit if material from the lead plates sheds and accumulates at the bottom of the cell, causing the reaction to stall. This is the primary reason cells die, as thousands of discharges and recharges inevitably lead to build-up. Battery lifespans depend on how many times they can discharge before too much material shorts a cell.

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