The Truth About Car Battery’s Magic Eye

The magic eye of a car battery is there to check on the condition of your car battery. But how reliable is the magic eye indicator?

Sometimes you will come across a dead battery even when the magic eye is telling you that the battery is healthy. Is this blog, we will explain to you the function of the magic eye and why you should not depend solely on its indicator.

Anatomy of the Magic Eye

There are 4 main parts of a magic eye. Only the head and ball of the magic eye are visible to you. The colour you see in the magic eye’s indicator is actually a ball place inside the car battery. 

Magic eye anatomy

How Does the Magic Eye Work?

The coloured ball will float when its surrounded by the well-charged electrolyte in the car battery. On the other hand, the ball will sink when the electrolyte is under-charged. Another phase is when the electrolyte is at a low level where you will see a clear magic eye.

Magic eye indicator


A pretty simple mechanics. But why can’t we rely 100% on the magic eye to tell the condition of a car battery?

Construction Of A Car Battery

If you notice, there are 5 to 6 vent plugs on top of a car battery. These vent plugs are designed to fill the car battery which is made up of 5 to 6 individual plate compartments.

Car battery construction
However, the magic eye will only show you the condition of a single plate compartment. So, when the magic eye tells you that the battery is in good condition but you can’t start your car, there are possibilities that the other plate compartments are in a bad shape.

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In short, the magic eye is not really reliable and definitely not accurate in measuring a car battery’s health.

How To Check Your Car Battery’s Condition

The most accurate way to check your car battery’s condition is using a multimeter. Even better if you use a dedicated battery tester. 

Check the battery condition readings, check the car’s charging system, and check again the battery’s readings.

A good battery should be able to keep its charge overnight at 12V and above without a problem.


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