Why does my car battery keep getting drained

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Why does my car battery keep getting drained
Testing battery voltage using a digital multimetre

By Okello Samuel

There could be more than one reason for a car battery to drain. The most common problems however are:

Parasitic Drain - If the electrical devices in your car or the lights on your car are left running even when your ignition is off, they will suck the juice out of your battery slowly but dramatically. This is often eerily described as a parasitic drain.

Defective charging system - A car battery drains quickly if something called the alternator on your charging system fails to push out enough voltage, ideally between 13.5 and 14.5 volts. In this case, the battery will continue to drain even while the car is running.

Defective alternator diodes - Alternatively, the alternator could have defective diodes which would drain the life out of your battery.

Extreme weather - If it’s too hot (above 100 degrees Celsius) or too cold (below 10 degrees Fahrenheit) your car battery could be damaged. Leaving your car in either condition for a long time would cause sulfate to accumulate, leading to a shorter battery lifespan.

Old battery - The average lifespan of a car battery is about 4-5 years, so it may be that your car battery is too old to hold a full charge.

Basically, the major reasons for battery drain are “Electrical devices or lights left running, a defective charging system or alternator, and extreme weather are some common reasons but maybe it’s just time to get a new battery.”

Signs of a dying car battery

If your vehicle has a battery marked with LOWER and UPPER on its side, you can check the electrolyte level, which should ideally be between the LOWER and UPPER mark. Other most common signs of a dying car battery include:

Before Startup


  • The gauges and lights don’t turn on when you turn the key for ignition
  • Jumping your battery every 3-5 days or even more frequently
  • Battery death within 15-30 minutes of idling with the engine off while other accessories are running

During Startup


  • Three or more turns for ignition
  • Dimming lights and/or accessories before startup
  • Greater difficulty in startup after idling for long hours, especially in the cold

During Driving


  • Slightly rough stops for traffic
  • Intermittent shutdowns of the radio and/or other accessories
  • Dimming lights and/or accessories when the accelerator is pressed



B.Eng. Automotive and Power Engineering

Technical Director

S-Line Motors LTD

Plot 6, Ojara Close, Mbuya


0779745722 / 0708000888


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