Why Does a Car Battery Need Water?

All car batteries contain water to help generate electricity for the car through the electrolyte solution (mixture of water and acid). However, the type of car battery you have will determine if you need to add more water to them over time. Read on to find out what type of battery you have and why your battery needs water to be added to them.

What type of battery is in my car? 

There are two main major car battery types which are maintenance-free and non-maintenance-free.

  • Maintenance-free batteries: these can also be referred to as sealed lead-acid batteries. They can easily be identified by not having filler caps on them. The battery is encased in a large unremovable flat cover which is mainly labelled maintenance-free. Therefore, the electrolyte in these batteries cannot be changed, and they are more susceptible to damage due to overcharging.
  • Non-Maintenance-free batteries: they can be easily identified with removable six filler caps on them and referred to as wet cell batteries. These batteries handle overcharging better because the water lost during charging can be replaced. This is a standard battery type as it can easily be managed.
car battery needs water

Why does a car battery need water?

A car battery comprises a lead plate and an electrolyte solution. The electrolyte solution in the battery is a mixture of water and sulfuric acid. As we can surmise from above, a battery already contains water, so why does the car battery need water again? When charging the battery, the electrolyte solution is being heated, and this causes loss of water due to evaporation. This reduces the density of the water inside the battery, increasing the concentration of the acid inside the battery.

How do you know when your car battery needs water?

 When the water in the battery is low, it can affect the car’s performance. Here are some of the things to watch out for to know if the car battery water needs to be topped off:

  • Reduced capacity: the electrolyte within a water-acid balanced range aids the battery’s optimal performance. Reduction in water leads to an increase in acid concentration which makes the battery be out of charge constantly.
  • Battery Indicator: Some battery has a battery level indicator on them. If the indicator glows green, the water level is okay, and the battery is charged. If it glows black, it means the battery needs fluid or is discharged, and if it glows yellow, it usually means the battery fluids are low or the battery is defective.
  • Using an external level indicator: there are indicators designed to help you check the water level in the battery. They tell you when the water needs to be topped up. Also, you can use a battery gauge which tells you the amount of water left.
  • Slow-cranking: with low water, the electrolyte will not have enough concentration to conduct electricity due to sulfate build-up. This can essentially lower the battery’s output and lead to the car’s starting problems. If left on checked for a long time, it can effectively start affecting the electrical components in the vehicle like the A/C, window, radio, etc.
  • Checking the electrolyte level manually: Another way to check the water level is by removing the filler cap and looking inside the individual plate cell. If the lead plate cell is not immersed, the water needs to be topped until it’s about ½ way above the internal plate.

How often should you add water to your car battery?

There is no specified time required for you to add water to your battery, but it may be frequently based on how often you use the battery. Some of the factors that can determine frequent are:

  • The age of the battery
  • The quality of the battery
  • The weather or temperature of the season
  • The usage of the battery

It is essential to regularly check the battery water level, preferable after the battery is charged. If you notice the battery needs a lot of refills in a concise amount of time, it may be best to consult with a professional.

How to add water to a car battery

Knowing that your battery needs water is not enough. There is a step-by-step method to add water to the battery without damaging it or getting hurt in the process. Here is a run-down of how to add water to a car battery:

  • Access the battery: the first thing to do is disconnect and take out the battery from the car. Ensure you’re wearing protective gear as the acid spill can be dangerous.
  • Clean before you open: Debris and other dirt particles would have accumulated on top of the battery over time. This dirt can enter the battery and cause contamination to the fluids. So, clean the battery head before opening the battery.
  • Open the filler cap: open the six caps of the battery and observe the electrolyte inside each cell. If the level is low, the water needs to be topped up.
  • Refill the water level: add distilled water to each low cell. The water level should be about ¾ below the top of the cell. This is to prevent damage to the battery as overfilling can cause damage. Recheck each cell to make sure enough water is added, then replace the cap and flush the head of the battery for any acid residue before returning the battery to the car.

What kind of water do you put in a battery?

The only kind of water used to top up a battery is distilled water due to its purity. It is not advisable to use tap water to top up your battery as it contains minerals that are very harmful to the battery, even if added in a small amount.

Precautions to take when adding water

When adding water to your battery, there are some steps that you should avoid as not to damage the battery. Some of them are listed below:

  • Wear protective gear to prevent acid spillage
  • Do not use tap water to refill your battery
  • Clean the top of your battery for dirt before you open it up
  • Do not underwater or over-water the battery. Use appropriate measurement always.

Tips for adding water to a battery

These are a few tips you should take note of when adding water to a battery:

  • Always use clean distilled water
  • Remember to check the water level and refill 
  • Consult the battery manufacturer specification to know battery capacity and fluid level requirements
  • In a hot climate, check electrolyte levels frequent as the hot temperature causes fluid depletion
  • Consult with a professional if you think you need help refilling your battery.


Adding water to a battery is relatively easy and not expensive, making it an obvious choice when your battery shows signs that it needs water. Knowing how to check electrolyte levels and refill the battery water can be the difference that prolongs your battery life. Take note not to allow dust to enter the battery or add tap water to your battery, and if you think you can’t handle it alone, it’s better to get professional help.

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