How To Check Car Battery Water Levels

Checking water levels of your car is very important to function well of your battery..

One of the things I’ve learned since I became obsessed with batteries is how to check car battery water level. You might ask, why am I preoccupied with batteries or better yet, when did I start to be hooked on batteries. Well, when I had to replace the battery of my four year-old car I took it upon myself to learn as much as I can about batteries.

How do you check the water level of a car battery? All you need to do to check the water level of the battery is to remove the vent caps covering the terminal posts and peek through the filler holes. If necessary, you can use a flashlight to see the condition of the water level more clearly.

What Do You Want To Know In Checking The Water Level Of The Battery?

First, let us be clear about one thing. Water is used here as synonymous to the electrolyte, a sulfur and water solution that is a vital component of your car battery. It is what makes the battery function. Without the electrolyte, your battery won’t work. The amount of electrolyte in proportion to the size of the battery plates dictates the amount of charge the battery can hold.

You check the water level of the battery to know if it still at least a half inch over the top of the separators and battery plates. If it is, it is an indication that your battery is still okay. If it isn’t, then it is time for you to top it off. If the water level is way above the top of the plates, then it has to be reduced to its normal level.

Regularly checking the electrolyte level is an important aspect of maintaining a wet or flooded lead-acid car battery. I specifically mentioned wet or flooded since the valve regulated lead-acid battery like an absorbent glass mat (AGM) battery is maintenance free and does not need topping off.

Going back to the importance of checking the electrolyte of a car battery, the water level of a battery subsides because the electrolyte of a battery evaporates naturally. It is also reduced because a small amount of it dissolves into oxygen and hydrogen when you charge the battery, The worst reason for a decrease in the car battery water level is a leakage.

When the battery leaks because of damage such as a crack in the casing or because of overcharging, then it is in serious trouble.

Maintaining the electrolyte in its normal level will help prolong the life of the battery. It could even help prevent critical battery failure.

Check the electrolyte level of your car battery as a routine maintenance practice and refill it with distilled water if the level is low. This should also be done if you notice a decline in the battery’s efficiency.

The battery of your car is used to store and deliver electricity to start the engine and help the alternator in operating the numerous electrical devices of your car. The electrolyte is responsible for the electrochemical reaction that produces the electricity.

Checking the electrolyte level of your car should be part of a regular maintenance program to guarantee good performance from your battery and engine.

When Do You Top Off The Electrolyte

Topping off means replenishing the electrolyte with distilled water and restoring it to the acceptable level which is the top of the plates or at least a half inch above the plates. If the electrolyte level falls below the tops of the plates, the battery can be damaged beyond repair. The only way to really know if your battery needs a top off or refill is by checking the water level.

You can check your car owner’s manual for suggestion or recommendations coming from the manufacturer as to when and how often to replenish the water on the car battery.

If you often charge and recharge the battery, you will need to check its water level also quite often. The battery loses water during every charge and discharge.

Another factor that should be considered in the frequency of checking and topping off a car battery is the temperature. High temperature, especially in a warm or tropical area, causes the water to evaporate faster. Thus, there is a need for a more frequent checking, and topping off if needed.

Top off or replenish the electrolyte with distilled water only, never with tap water. Tap water contains substances that could be harmful to the battery, diminish its performance and increase the rate of self-discharge. (Check how to make distilled water).

Also, always make sure that your battery is fully charged before topping it off.

In topping off the electrolyte, beware of the following:

● The electrolyte level of some new batteries can, at times, be low. Charge the battery first before adding distilled water if needed. If you refill the electrolyte before fully charging the battery you might have an electrolyte overflow.
● Beware of overwatering the battery. In doing so, you could dilute the electrolyte which could result in a decrease in the battery’s performance level.
● Be careful not to underwater the battery. Underwatering could cause sulfation, the build-up of crystal sulfates on the battery plates. Sulfation leads to loss of power, a longer time to charge, and a major cause of battery failure.
● Avoid charging at a lower voltage. Although charging using a lower voltage could lessen the need to top off the electrolyte since lower voltage means lesser water loss, it could also cause stratification. This is the most prevalent adverse effect of charging using a lower voltage.

The electrolyte stratifies when its acid content separates from the distilled water and sink at the base of the battery. Stratification is another cause of sulfation, the accumulation of sulfate crystals in the plates. Sulfation is very bad news for your battery and should be avoided at all cost if you want to maintain the capability and lengthen the life of your battery.

How To Top Off A Car Battery

First, you check the water level of your battery through ocular inspection via the vent caps of the terminal posts. Once you observed that it is below the normal level or at least a half inch lower than the top of the plates, you must top it off or refill it to return it to normal levels.

Let me give you a step-by-step process of topping off a battery:

Step 1- Find the battery. Most cars have the batteries under the hood. However, there are cars, especially the newer and more expensive models, with batteries in other places other than under the hood.

Batteries of cars like a Mercedes Benz or BMW are found in the trunk, segregated in a confined space. Some cars have their batteries in the lower portion of the engine compartment, at the back of the front bumper and before the front wheels, while others have their batteries beneath the rear seat or behind the wheel well.

Step 2- Clean the battery. Once you find the battery, clean the top and the area surrounding the battery terminals of dirt or corrosion. This step is vital since no foreign substance like grime and corrosion should enter the cells once you open it.

Remove the dirt and light corrosion by wiping it off with a rag dampened with an ammonia-based window cleaner. If the corrosion is quite heavy, apply a mixture of water and baking soda on the surface to be cleaned, and brush off the corrosion with a steel brush. Wipe off the residue of the baking soda mixture with the rag sprayed with the window cleaner to prevent corrosion in the future.

At this stage, make sure that the vent caps of the terminal posts are still in place. Never allow even a speck of dirt or a drop of the cleaning solutions trickle or flow inside the battery.

Check for more information.

Step 3 – Remove the battery from the car. It will be safer to remove the battery from the car when you top off the electrolyte, especially if it is located in a cramped and unwieldy location.

Step 4 – Remove the vent caps covering the terminal posts to open them. For this purpose, you can use an appropriately sized socket wrench to loosen the cap, and once the cap is loose, remove it with your hands.

Reminder: You should be wearing rubber gloves as well as other safety gears like goggles, and a long-sleeved shirt to protect your skin while working on the battery.

Step 5 – Continue cleaning. Once the vent caps are removed and the ports are open, there might still be grime and dirt on the surface of the battery. Remove the grime and dirt using only the rag sprayed with the window cleaner and not the baking soda solution.

See to it that nothing enters the port – not the dirt, the cleaner, bits of rag, totally nothing.
Don’t do any shortcut and skip this cleaning process. It is a very important element of your battery maintenance. Keeping the battery clean will prevent corrosion in the future and safeguard the integrity of the connection.

Step 6 – Inspect the water level. Check the electrolyte levels of each cell by peering through the ports. The water levels of the cells must be the same, and it should be at least half an inch above the plates.

If the fluid contents of the cells are unequal or you observe that the water level is below the normal and the plates are slightly exposed to the air, then a refill is in order.

Step 7 – Top off the Electrolyte. Fill the cells with distilled water using a funnel until the normal level is reached. Do not overfill or underfill. Keep in mind that the electrolyte should be at least half an inch above the top of the plates.

Step 8 – Close the vent caps and return the battery back on the tray. Once you have finished refilling the electrolyte, replace the vent caps and close them securely. Wipe dry any spill with the rag, then return the battery back to the car.


Checking the car battery water level is an important aspect of car battery maintenance. If you want to prolong the life of your battery and keep it at top performance, make sure that the electrolyte of your battery is always at a normal level.