Why Do Car Batteries Need Water?

Image: Shutterstock.com

Much like humans use water to regulate bodily functions, a vehicle’s battery fluid levels need to remain at a safe level for it to function properly – and sometimes this requires refilling the battery fluid. Not all types of car batteries need to be refilled, so it’s important to know what type of battery is in your vehicle. If your battery does require some maintenance, it is vital to understand how to check if the water needs to be refilled.

When a vehicle’s battery is running and charging, battery fluid is converted to gas and then evaporates. Conventional batteries utilize a liquid electrolyte, a combination of distilled water and sulfuric acid. Low water levels expose plates inside the battery, causing battery sulphation and limiting the flow of current through the electrolyte.

Neglecting your car’s battery maintenance significantly reduces its lifespan and results in progressively shorter run times between charges. To prevent the untimely failure of your vehicle’s battery, it is important to understand the basics of maintaining your battery’s water level and any external factors that could negatively impact your car battery.

Getting to Know Your Car’s Battery

If you’re unsure whether your car battery’s water needs to be topped up, it’s time to pop the hood! Some modern cars have what is called a maintenance-free battery, while a majority of cars use what is called a wet-cell or non-maintenance-free (NMF) battery. As the name suggests, NMF batteries require occasional maintenance.

Having a look under your car’s bonnet is the quickest and most efficient way of identifying the type of battery your car uses. If your car has an NMF battery, it will be easily identifiable by a filler cap on the battery. Maintenance-free batteries are sealed by a fixed cover, and fluid levels cannot be checked.

Before unscrewing the cap/s, check if your battery features an LED water-level indicator. If this is the case, the indicator will glow green when the water level is good and yellow if the fluid level is too low. In some cases, a yellow light could indicate that the battery is faulty. Whether you have a maintenance-free or NMF battery, it is crucial to get your battery tested occasionally to make sure it is performing well

If your battery has a flat refill cap and no indicator, the fluid level can be checked by peeking below the cap. Before doing this, make sure the battery’s exterior is clean to prevent contamination of the water inside the battery. To do this, use a solution of baking soda and warm water made to a 1:4 ratio in a glass, respectively. Safety gloves and goggles are also recommended for this, in case of accidental exposure to battery acid.  

Use a plastic scraper to pry open the flat caps on the battery, which should reveal a row of small holes. As a general rule of thumb, your battery’s water level should be at least a half-inch above the battery’s internal plates or about a half-inch from the top of the battery.

The plates, when seen from above, are akin to the folds of an accordion and are typically a gray color. If you find that the water level needs to be topped up, it is important to use the correct type of water and to follow the instructions carefully for your safety.

How Frequently Should You Check Your Battery?

If you need to open up your car’s bonnet to locate the battery and check if it’s a maintenance-free or NMF battery, chances are you haven’t checked your battery before this point. Now you’re wondering, how often should I be checking my battery’s fluid levels?

The frequency of battery checks should typically be proportional to the usage of the relevant vehicle. If it’s a vehicle only being used a few days a week for shorter periods, the battery’s fluid levels may only need to be checked and topped up once a month. If the vehicle is used every day for long periods, you may need to check your battery every week.

Where you are situated and what the climate is like there will also have an effect on your car’s battery and how often you should check it. If you live in a hot climate like that of the Middle East – or you’re experiencing a summer that makes you feel like you live in the desert – then you’ll want to check your battery’s fluid levels more often as the heat increases the speed of evaporation.

In lower temperatures, you’ll want to check on your batter, too. Vehicle batteries work harder to start in colder climates due to the thickening of motor oils as a result of the weather. 

While getting into the habit of checking your battery, it is better to check it more frequently during the first few weeks. Doing this will better allow you to gauge how much water your battery consumes, which will be dependent on the factors discussed above. This will aid you in knowing how often you should be checking your battery’s fluid levels based on the above-discussed criteria.

Image: Shutterstock.com

How to Correctly Replenish Your NMF Battery’s Water Levels

You’ve located your car’s battery and determined it needs to be topped up with water, now to get those latex gloves a bit dirty! As previously mentioned, make sure to wear gloves and goggles to prevent contact with battery fluid, which could result in serious burns. Overwatering or giving too little water can damage your vehicle’s battery, so be sure to follow the instructions carefully.

  1. Prepare a mixture of ¼ cup baking soda and one quart of warm water.
  • Make sure the vehicle’s engine is turned off and has cooled down.
  • Make sure that the battery is completely charged. If there is no indicator on your battery, you can:
    • Use a voltmeter, which should read 12.6 volts with the engine switched off and the battery fully charged.
    • Use a battery hydrometer, which should have a pH reading of 1.265 or higher when the battery is fully charged.
  • Use a brush (an old toothbrush will work) with the mixture made in step one and clean the battery housing. Once done, flush with clean water and pat down with a paper towel before removing the filler cap.
  • Pry off filler caps using a plastic scraper. Once the vent caps have been removed, clean around the holes carefully using a paper towel.
  • Peek inside the filler holes and check whether the water covers the top of the battery plates.
  • If the water level is low and the battery plates are exposed, you will need to top the water up with distilled water until the plates are covered with water.
    • Do not use tap water, as it contains certain minerals that will damage your battery.
    • Do not overfill with water and make sure not to splash while performing the water top-up. A measuring jug or food baster can help you control the flow of distilled water into the cell holes.
  • Replace the battery’s vent caps securely and throw away your gloves!

Signs Your Battery Needs More Than Water

Your car battery will deteriorate over time, leading up to that dreaded morning when the car won’t start because it cannot produce enough power to start the engine. When properly maintained, a car battery has a typical lifespan of 3 to 5 years, though this depends on a few key factors.

Your vehicle’s usage pattern, as discussed earlier, plays an important role in the lifespan of your battery. If you only drive short trips with your car, you risk not fully charging the battery, which can weaken it over time and shorten its lifespan. The role of temperature on a car battery was also previously discussed and, because of this, the same car battery that lasts 5 years in a cooler climate would only last about 3 years in a hotter climate.

When it’s inevitably time to replace your car battery, there are clear signs to look out for. If you have a suspicion your car starting up as fast as it used to, or you notice that your headlights seem dimmer, then it might be time to get your battery tested. Once your battery turns 3 years old, it’s time to get it tested annually!


Battery maintenance is only one part of maintaining a car, but it’s an important one as the battery powers everything else. Identifying what type of battery your car uses – be it a maintenance-free or non-maintenance-free battery – tells you how to care for your car’s battery.

It is also crucial to understand the other factors that could negatively impact your vehicle’s battery, such as temperature extremes, and how to mitigate these effects by regularly checking the fluid levels. Make sure to use precaution when refilling your batter’s water levels, and to only use distilled water. With the proper maintenance, you’ll get the most out of every battery!