Blog Car Care Advice Battery Water: How To Add It & Check It + 6 FAQs
Car Care Advice

Battery Water: How To Add It & Check It + 6 FAQs

Looking for a mechanic near you for maintenance or repair? AutoNation Mobile Service brings the shop to you. Get a free instant quote today.
Get a Quote

Conventional lead acid batteries are popular for a reason. 

They’re cheap, long-lasting, and considerably low maintenance. 
However, a very important part of their battery maintenance is refilling them with battery water. 

But what exactly is battery water? 
And how do you use it? 

In this article, we’ll answer those questions and cover the potential problems you can expect with battery water. Then, we will cover how to add water to a car battery and other related queries you may have. 

This Article Contains: 

Let’s get right into it!

What Is Battery Water?

Your flooded lead acid battery consists of a fluid solution called ‘electrolyte.’ This solution is used to charge your batteries.

But is battery water the same as the electrolyte solution?


The electrolyte in your battery is a mixture of sulfuric acid and water. Battery water, on the other hand, is the clean water used to refill the electrolyte when its levels run low.

The water used in battery water is usually distilled water or deionized water. It’s never tap water, as tap water may contain impurities.

What Does Battery Water Do?

Your flooded battery works with the help of the electrolyte solution. 

Every time you charge the battery, inevitably heating the electrolyte solution, the battery electrolyte experiences water loss due to evaporation. This affects the density of the battery water level and increases the concentration of sulfuric acid at the same time. 

If you do not water the battery again, the excess sulfuric acid will ultimately lead to sulfation and irreversible corrosion.

This is where battery water comes into the picture. 
Distilled water is added to the electrolyte solution to prevent low electrolyte levels, and maintain the concentration of sulphuric acid in the solution. 

With that said, how exactly do you go about watering your battery?

How Do I Water A Car Battery? 

Here is the step-by-step guide on how to properly water your car battery: 

  1. Start by wearing the appropriate safety gear.
  1. Disconnect the battery. Remove the vent cap and clean the surface around the battery terminals. This will prevent dirt from getting inside the battery.
  1. Open the battery cap and inspect the fluid level. The battery terminals in each cell should be fully immersed in the liquid.
  1. Observe the electrolyte solution and check if the battery water level is low, normal, or maximum capacity. 
  1. If the levels are low, pour just enough distilled water to cover the lead plates. Make sure you use your battery charger and charge it before filling it with clean water. 
  1. For older batteries, never fill them up to maximum battery capacity. These are very quick to overflow, causing further damage and corrosion.
  1. Once done, close the vent cap and the battery cap, and seal them shut. 
  1. If you see any overflow, clean it with a rag. 
  1. If you feel like you accidentally overfilled the battery and expect a boilover, let the battery be. Check back after every two days to see for any signs of an overflow and water loss. If yes, wipe it off. 

Note: Remember that this procedure only applies to flooded lead acid batteries. 
You cannot add battery water to an AGM battery since these types of batteries tend to be maintenance-free. 

Read more about this in our AGM Battery vs Lead Acid Battery guide

How Do I Check My Car Battery’s Electrolyte Levels?

Once you open the vent cap and battery cap, you will be able to observe the individual lead plates in each cell. 

You will always notice three types of electrolyte levels in rechargeable batteries. 

They are:

Next are some things you need to be careful of when dealing with battery water.

What Are Some Problems To Avoid With Battery Water? 

Not being prompt with battery care can cause serious short-term and long-term problems to your battery’s lead plates and other components. 

Here are some of the problems you might face if you’re not careful with battery maintenance:  

1. Low Electrolyte Levels

A low electrolyte level is when the liquid in the batteries runs too low and may potentially expose the lead plates to oxygen. 

Sometimes, brand new batteries tend to have low levels of electrolyte. In this case, you may want to first charge them using a battery charger and then add some more water. 

If you add more water before the battery is fully charged, there will be no room left for the liquid to expand once it is heated. This runs the risk of electrolyte overflow and is dangerous for your battery’s health. 

You may also dilute the electrolyte even further, thus causing irreparable damage to the battery. 

2. Underwatering

Underwatering is when you fail to refill the battery when it reaches a low electrolyte level. 

Each time you charge your battery, the battery cell will experience a further water loss. If the water level reaches as low as to expose the lead plates to oxygen and hydrogen gas in the battery, it can lead to sulfation

Here are a few ways to avoid it:

A sulfated battery severely affects the performance of your car and can be dangerous. Sulfation is preventable, but it is important to ensure proper battery maintenance and regular battery checkups. 

Note: People often wonder if they can lower the charging voltage of the battery to reduce the need to water it. While this may work, it is dangerous for your battery to have a low voltage. Low energy storage and voltage can cause serious battery damage and premature battery failure.

3. Overwatering 

As the name suggests, overwatering is when you add excess battery fluid to your electrolyte solution. Consistent overwatering can cause severe damage to the battery cell, and you may also notice a significant drop in performance. 

Overwatering may lead to two problems: 

Firstly, it will dilute the electrolyte solution in the battery. This will reduce your battery’s performance since it won’t have enough charge to operate. 

Secondly, if you water the battery before appropriately charging it, the water will boil over. This is because when the battery is charging, the liquid will get hot and expand. If it does not have enough space, the battery acid will spill out of the battery. 

You may also take the specific gravity readings to determine the charge of your battery. Specific gravity and charging voltage will give you an idea about the battery life and overall health. 

We’ve now covered all the basics of battery water and how to use it. Let’s now look at some common battery water questions and their answers. 

6 FAQs About Battery Water

Below are some frequently asked questions about battery water and their answers:

1. How Does Battery Electrolyte Work? 

Electrolyte plays a key role in generating electricity for rechargeable batteries. 

Here’s how it works in a flooded battery (lithium batteries work differently): 

2. How Often Should I Water My Car Battery?

How often you should water the battery will mainly depend on how often you charge it. If you use your car a lot, you will need to charge the battery quite often. This means that the water in your acid batteries will evaporate faster. 

For example, a forklift battery will demand a very different charge cycle than a deep cycle battery. This is because forklifts tend to use maintenance-free batteries or waterless batteries, while deep cycle batteries are usually flooded. 

Plus, hotter temperatures aid the evaporation of the water. 
This is why summers require frequent battery watering. 

It is best to check for signs of low electrolyte levels from time to time. Once you get an idea of your battery power and charge cycle, you can form a routine. 

3. What Type Of Water Should I Use For My Car Battery?

Always use distilled water or deionized water for your flooded battery, and never tap water!

Tap water often contains small amounts of minerals, chlorides, and other impurities that can react with sulphuric acid and harm your battery. These impurities may react with the battery plates, and battery owners should avoid this during lead-acid battery maintenance. 

4. What Happens If A Lead-Acid Battery Runs Out Of Water?

If that happens, the lead plates will be exposed to the existing oxygen and hydrogen gas in the battery. This exposure will cause an exothermic reaction with the battery terminals, emitting huge amounts of heat. 

The heat will further evaporate the water. In the long run, this will lead to irreparable damage to the battery cell. 

5. What Is Sulfation?

Sulfation is the excess buildup of lead sulfate you see on your battery plates. It’s one of the most common problems you can face with a lead battery. 

It is caused due to a variety of factors including, a low electrolyte level, overcharging, and undercharging. 

If you’re frequently charging your battery to limited potential, instead of fully charging it, you may be exposing the lead plates to sulfation. This lead sulfate can cause irreversible damage to your battery plates and battery capacity. 

6. What Safety Measures Should I Follow While Adding Battery Water to My Car?

Here are the safety measures you should follow while adding battery water:

Final Thoughts

Sometimes, battery damage is unavoidable and is bound to happen as it gets old. 

However, problems caused by low electrolyte levels are very easy to prevent. Regular refilling and checkups will keep your battery’s health in check. And as battery owners, your wallet will thank you for it. 

The best way to ensure the overall smooth functioning of your car is to maintain it right — irrespective of whether it uses a conventional lead battery or is an electric vehicle with a lithium-ion battery. 

If you ever need professional help, AutoNation Mobile Service is just a few clicks away! Contact them, and their expert technicians will be at your driveway to help in no time.