Our mechanical engineer answers a few battery-related questions.

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Our mechanical engineer answers a few battery-related questions.

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HOW often do I need to change my car’s battery? With stop-start systems, is there more wear on the battery and starter motor?

Generally, car batteries should last at least one year, although neither car manufacturers nor battery-makers ever declare a battery’s lifespan. 

Try to replace your car’s battery with a maintenance- free battery which has an indicator showing its state of charge, so that you can be aware of its health. 

If you seldom open your car’s bonnet, then the best advice is to replace your car’s battery every year, but that does not mean car batteries have a lifespan of only 12 months. 

These days, many cars come with stop-start systems, which demand more electrical energy. Such cars have more efficient alternators, heavy-duty starter motors and specially designed batteries.

The alternator is designed to cope with frequent starting and, hence, charges the battery more rapidly. It is the same with the starter motor, which is built to sustain frequent starts without overheating. 

More importantly, where a stop-start system is installed, a controller manages stop- start activity based on battery state and will never allow the system to operate if a low- energy level is detected. 

Stop-start systems, therefore, do not demand significantly higher maintenance. 

But you should take note that batteries used in cars with a stop-start system are costlier. They use either Enhanced Flooded Battery technology or Absorbent Glass Mat batteries. 

Neither technology is new. Absorbent Glass Mat batteries have been used in industrial machines for some time and are commonly found in emergency generator sets. 

Does a car with a stop-start system have a higher chance of stalling? Some of these cars come with notices on the sunvisors advising what drivers should do if the engine does not restart.

This is a bit of an irony because stop-start systems go through periods of “stalling” that are independent of the driver or the condition of the engine. 

Uninitiated engine shutdown is now standard fare in a number of cars, incorporated to reduce fuel consumption when waiting, as at traffic light junctions. 

When this occurs, your engine has effectively “stalled”. Start-up is automatic the moment you release the brake pedal. The feature can be deactivated by the driver.

However, some motorists are concerned that the engine will not restart when it should. 

If the engine indeed does not start up automatically, then switch off the ignition and start up as you normally would. Ensure the transmission is in Neutral or Park when doing this. 

Stop-start systems are designed with a number of fail-safe features to prevent a total shutdown. For example, when the battery is weak, stop-start will not activate. 

For now, there is no hard evidence to suggest that a car with such a system has a higher chance of stalling.

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What are the possible reasons for erratic idling? Also, I have noticed that at night with the headlights on, the idling speed slows down even more, while the lights stay very dim and brighten considerably only when I rev the engine.

Is this an engine problem, an electrical problem or both?

The most likely cause for the symptoms described above is a low voltage supply.

This will often cause the engine control unit to function a little abnormally, resulting in a lower than normal idle speed. Low voltage will definitely cause lights to be dim, too.

The first thing to check in rectifying the problem is the condition of the battery. If it is weak, replace it immediately.

Sometimes, the problem may just be loose battery terminal connections. Make sure these are clean and tight.

Often neglected is the earth cable that runs from the negative battery terminal to a secure point on the car’s body or chassis. Many electrical problems are caused by a weak earth connection. Have the cable checked and replaced, if necessary. It can deteriorate over time.

Finally, check the condition of your vehicle’s alternator, which should supply 14 volts to the battery when the engine is running at its normal idle speed.