Here are the eight main things that go wrong with car batteries:
- Short-circuited cell due to failure of the separator between the positive and negative plates.
- Short-circuited cell or cells due to a build-up of shed plate material below the plates.
- Sulfation after a long period of disuse in a low- or no-charge state.
- Corrosion or damage to the positive and negative terminals.
- Broken internal connections as a result of corrosion.
- Broken plates due to corrosion and vibration.
- Damage to the battery case.
- Low electrolyte (fluid) level.
How does my car battery work?
Lead-acid car batteries are made up of plates of lead and lead dioxide submerged in an electrolyte solution of about 35 per cent sulphuric acid and 65 per cent water.
During discharge, such as when the battery is used to start the car or power the headlights, the sulphuric acid in the electrolyte is depleted, leaving an electrolyte solution with a higher proportion of water. Sulphate from the acid coats the plates, reducing the surface area on which the chemical reaction can happen. Charging reverses this chemical reaction, returning the sulphate to the acid.
The lead-acid battery’s high power for its weight, along with its low cost, makes it attractive for use in cars. This type of battery is capable of providing the high current required by the starter motor to crank the car’s engine.
The battery stores energy to be released in order to start the engine. Once the engine is started, your car's battery is recharged by the engine-driven charging system – the alternator takes energy from the rotation of the engine via a belt drive to supply the charge current.
Corrosion at the battery terminals is a very common cause of a car that won’t start. The corrosion, which often takes the form of a white powder (lead sulphate) adds resistance, reducing the amount of electrical current that can get to the starter motor.
Cleaning the terminals periodically using water and a wire brush will prevent this, but make sure you wear gloves and eye protection because the white powder is toxic and should not be inhaled, ingested or allowed to come in contact with your skin.