How a Battery Works?

How a Battery Works?

The principle of how a battery works is based on a scientific principle discovered years ago that states:
-When two dissimilar metals are placed in an acid, electrons flow between the metals if a circuit is connected between them.
-This can be demonstrated by pushing a steel nail and a piece of solid copper wire into a lemon. Connect a voltmeter to the ends of the copper wire and nail, and voltage will be displayed.
A fully charged lead-acid battery has a positive plate of lead dioxide (peroxide) and a negative plate of lead surrounded by a sulfuric acid solution (electrolyte). The difference in potential (voltage) between lead peroxide and lead in acid is approximately 2.1 volts.

The positive plate lead dioxide (PbO2) combines with the SO4, forming PbSO4 from the electrolyte and releases its O2 into the electrolyte, forming H2O. The negative plate also combines with the SO4 from the electrolyte and becomes lead sulfate (PbSO4).

When the battery is fully discharged, both the positive and the negative plates are PbSO4 (lead sulfate) and the electrolyte has become water (H2O). As the battery is being discharged, the plates and electrolyte approach the completely discharged state. There is also the danger of freezing when a battery is discharged, because the electrolyte is mostly water.

During Discharging

During charging, the sulfate from the acid leaves both the positive and the negative plates and
returns to the electrolyte, where it becomes normal-strength sulfuric acid solution. The positive plate returns to lead dioxide (PbO2), the negative plate is again pure lead (Pb), and the electrolyte
becomes H2SO4 .

During Charging

CAUTION: Never charge or jump start a frozen battery because the hydrogen gas can get trapped in the ice and ignite if a spark is caused during the charging process. The result can be an explosion.

Is There an Easy Way to Remember How a Battery Works?
Yes. Think of the sulfuric acid solution in the electrolyte being deposited, then removed from the plates.
• During discharge. The acid (SO4) is leaving the electrolyte and getting onto both plates.
• During charging. The acid (SO4) is being forced from both plates and enters the electrolyte.


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