How to check the water levels in your car battery

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How to check the water levels in your car battery
How to check the water levels in your car battery

It's important to frequently check the electrolyte levels (actually, it's not just water) in your car battery for two reasons: first, because it evaporates naturally, and second, because a small amount is converted to electrolyte hydrogen and oxygen. every time you charge the battery. Knowing how to safely check and replenish your car battery water is an important aspect of car maintenance. Read the steps below to find detailed instructions on how to check your car battery water levels while protecting yourself and your car.


Part 1 of 4: Clean the battery and open the ports


Step 1. Locate the battery

On most cars, you simply need to open the hood to access the battery.

  • Some batteries are located at the bottom of the engine compartment, behind the front bumper and in front of the front wheels. Sometimes these batteries can be accessed from the bottom and need to be removed for maintenance.
  • Most BMW and Mercedes Benz batteries, and a few others, are located in the trunk, hidden in an isolated compartment.
  • The batteries could also be found under the rear seat, as is the case with some Cadillacs.

Step 2. Clean any traces of dirt

Before checking the water levels, clean any dirt or debris from the top of the battery and around the battery terminals. This is important, as you don't want any foreign material to get into the battery cells when you open them. This is also important, because a clean surface on a battery helps slow or stop corrosion on nearby metal.

  • For a general clean of dirt from the tracks and minor corrosion, use an ammonia-based glass cleaner. Spray the cleaner on a rag (not the battery itself) and wipe off any dirt. You can use paper towels, as long as you change them before they disintegrate.
  • You can clean up heavy corrosion with a paste of baking soda and water. Again, wet a cloth and clean; do not soak the battery in baking soda. Sometimes the cloth needs to be wetted and cleaned many times. Continue wiping with a cloth dampened with glass cleaner to remove the baking soda. Leaving a residue of baking soda on the outside of the battery will accelerate future corrosion of the terminals and nearby metal.
  • Do not get ahead. Make sure the covers are over the battery ports at this stage of cleaning. Do not let cleaning fluids drip or spill onto the battery through the ports.
  • Note:

    If you prefer, you can remove the battery from the car before cleaning and perform this maintenance to reinstall it later. This can be safer, especially if the battery is in an awkward position. However, this will zero out some or all of the car's electronics (the clock, pre-programmed radio stations, etc.). If you can check the battery without removing it from the car, this will generally save you considerable time overall.

  • You can also remove the battery terminals and submerge them in a cup of very hot water. The high temperature of the water will melt the corrosion and leave a clean surface. Make sure the terminals are completely dry before replacing them on the battery.

Step 3. Open the ports

On the battery, there are usually two semi-rectangular plastic covers that are used to seal each port of the battery cell. These can be gently removed by prying them apart with a plastic putty knife or screwdriver. Try to separate them from various points around the cover in case the cover doesn't come off immediately.

  • Some batteries have six individual round covers. You can remove them by turning them counterclockwise and then lifting them up.
  • If the battery is labeled "maintenance free", it is not designed to open. The manufacturers advise that you cannot add water to these batteries; they simply need to be replaced if they stop working well.

Step 4. Continue cleaning if necessary

Removing the port covers can expose more dirt on top of the battery. Continue cleaning the ports with a cloth dampened with glass cleaner.

  • Do not use baking soda for this cleaning. Use a small amount of glass cleaner and be very careful to prevent anything (cleaner, dirt, pieces of paper towels, etc.) from getting into the ports.
  • Don't be tempted to skip this step. Keeping the top of the battery clean will reduce future corrosion. This is an important aspect of battery maintenance to preserve the integrity of the connections.

Part 2 of 4: Assess Existing Fluid Levels


Step 1. Compare the fluid levels in each cell

Looking through each port, you can see the electrolyte level in each individual cell. Each cell must be covered by the same amount of fluid.

  • If this is not the case, it may have been caused by the simple fact of accidentally overfilling them earlier, in which case the problem is easily corrected by filling them correctly later, after the level of the overfilling cell has dropped to the normal level with normal car service.
  • If fluid levels are obviously uneven, it is also possible that the battery has a small fluid leak or a cracked container. If so, the battery needs to be replaced. If there are no obvious leaks, fill the battery to the maximum safe level using only distilled water and check again in a few weeks to see if the levels have remained consistent.
Check Car Battery Water Levels Step 6
Check Car Battery Water Levels Step 6

Step 2. Recognize when electrolyte levels are low

The electrolyte is too low if any part of the plates is exposed to the weather. If the plates are not completely covered in electrolyte, the battery cannot function at its maximum capacity.

  • Exposing the plates to the elements ruins the exposed area in a matter of days.
  • If the electrolyte is only about half an inch (1 cm) below the top of the plates, adding enough water to the battery to just barely cover the plates can bring the battery back into working order at capacity slightly reduced (instructions for adding water are in part 3 of this article). Otherwise, you will have to consider replacing the battery.
  • A low electrolyte level can be caused by overcharging the battery, so if this is the case, you should consider checking the alternator.
Check Car Battery Water Levels Step 7
Check Car Battery Water Levels Step 7

Step 3. Recognize when electrolyte levels are normal

The normal fluid level is about 1 cm (half an inch) above the top of the plates, or about 3 mm (1/8 inch) below the bottom of the fill tubes that are extend downward from the port openings.

If this is the case, it may not be worth the effort to fill the battery at this point. Simply replace the port covers and inspect again within three months

Check Car Battery Water Levels Step 8
Check Car Battery Water Levels Step 8

Step 4. Recognize when the electrolyte is at its peak level

The maximum safe fluid level is when the fluid just touches the bottom of the fill tubes.

  • Most filler tubes have a pair of slots on one side near the bottom of the tube. This causes the meniscus (the part of the fluid that bends near the edge of the tube) to have a distinctive eye shape if the fluid is touching the fill tube, while there will be no meniscus if the fluid is below the part. bottom of the filler tube.
  • The eye-shaped meniscus is designed as a signal to stop filling. You may need to use a flashlight to clearly see the fluid level and the presence or absence of the meniscus.
Check Car Battery Water Levels Step 9
Check Car Battery Water Levels Step 9

Step 5. Remember that these levels are for lead acid automotive batteries only

You should always follow the battery dealer or manufacturer's instructions in case they conflict with the information provided in this article.

Also keep in mind that batteries for golf carts and floor machines, as well as nickel cadmium batteries, in particular, may require other levels of electrolytes

Part 3 of 4: Adjust Liquid Levels


Step 1. Use only distilled water to fill the cells

You can buy distilled water in most supermarkets. If the electrolyte levels in the cells are low (plates are exposed), fill each cell to just barely cover the plates. Then use a charger to charge the battery or just drive the car for a few days in normal service. Only fill to the maximum safe level (just touching the bottom of the fill tubes) if the battery is fully charged.

  • Use a funnel, an isotonic drink bottle, a kitchen syringe, etc. clean to ensure flow control and final level accuracy when filling each port. Take great care to prevent any dirt or cleaning agent from entering the cells.
  • Using tap water, well water, filtered water, or anything other than distilled water will introduce minerals and chemicals (for example, chlorine if it is city water) and other contaminants that will result in a decrease in battery life.
Check Car Battery Water Levels Step 11
Check Car Battery Water Levels Step 11

Step 2. If the battery is weak or discharged, avoid filling the cells completely

If you are adding water because the battery is weak or discharged, it is best to fill it only enough to cover the plates (or leave it that way if it is at a normal level).

  • When a weak or discharged battery is charged, the electrolyte level rises. Therefore, you should allow room for the level to rise when you charge the battery (this does not happen with a fully charged battery).
  • Electrolyte levels can also rise if the battery gets hot.

Step 3. Clean up spills and close ports

Make sure all areas are clean and free of dirt or debris, then put the clean port covers back on the battery.

  • If you accidentally overfilled the battery, but it doesn't overflow onto the top surface, the best thing to do is simply stop filling it and leave it at that. If there is an overflow on the top of the battery, remember that it is acid, so do not let it come in contact with your skin or clothing.
  • Wipe it with a rag or rags, or with paper towels in the opposite direction of the ports. Don't let the rag or paper towels get wet enough to drip onto other parts of the car or anything else. Rinse the cloth or paper towel in a bucket of water. Wear gloves and don't let the water touch your hands.
  • After finishing the job, dispose of the rinsed rag or paper towel in the regular trash. Pour the water down the drain, being careful not to splash it. You don't want to risk the acid residue splashing on something. Finally, clean up anything that came in contact with the overflow using a cloth dampened with the glass cleaner.
  • Visually inspect any battery that has become overfilled every week for a month for any subsequent overflows and clean as described above, if necessary.
  • The sulfuric acid that the battery has lost due to an accidental overflow is probably a small enough quantity to be irrelevant to the operation of the battery. It is best not to try to add acid to make up the loss (too much acid shortens battery life more than too little acid).

Part 4 of 4: Take Proper Safety Precautions


Step 1. Protect your eyes by wearing goggles

The electrolyte in the battery is sulfuric acid, so it is extremely important that none of this liquid gets into your eyes, as it could cause significant damage or even blindness.

  • Contact lenses don't give you any protection and could complicate an accident. Regular lenses do not provide adequate protection due to the lack of side shields.
  • Therefore, it is essential to wear protective glasses, which you can buy at most hardware stores.

Step 2. Protect your hands by wearing disposable gloves

Choose a type of glove that can resist sulfuric acid for at least a few minutes. You can buy them at hardware stores.

  • Latex and vinyl gloves will not resist acid for long. If you wear latex or vinyl gloves, change your gloves immediately as soon as you notice a splash on them. As time goes on, a splash of electrolyte will seep through the glove and burn your skin.
  • Neoprene gloves offer protection for an hour or more, but are harder to find at regular hardware stores. Nitrile is not the same as neoprene. Nitrile gloves offer less protection from sulfuric acid than latex and should not be used.

Step 3. Protect your skin

Wear old clothes with long sleeves, long pants, and closed shoes to cover as much skin as possible. If some electrolyte splashes on your clothing, the fabric will break down in about a week or two, leaving a hole, so wear old clothing that you can sacrifice.


Step 4. Consider what to do if the electrolyte touches your skin

If some of the electrolyte splashes on your skin, wash it off immediately with soap and running water.

  • If you feel burning or tingling anywhere on your skin, a drop of electrolyte may have splashed on you. It only takes one drop to cause a burn.
  • You may not be able to see any redness or injury until it is too late, so if you suspect you may have splashed yourself, take a break from your work and wash immediately rather than risk it.
  • Throw away all used gloves and rags when the job is done. Leaving them in contact with other materials could cause damage.


  • If you don't know what you are doing, take your car to the mechanic. Most auto parts stores will perform this service for free.
  • Keep all areas free and clear of debris while you are servicing the battery.
  • Do not remove the battery port covers while the car is running.
  • Make sure to protect your eyes. Battery acid can blind you and is very corrosive.
  • Wear protective goggles when checking and filling battery cell fluid levels.
  • Use a 1 inch (2.5 cm) wide plastic putty knife to separate the port covers. Plastic putty knives can be purchased at most hardware stores or wherever house paint is sold. Alternatively, you can use a screwdriver with an insulated handle, but when separating the covers, be careful not to let the metal shaft of the screwdriver accidentally bump into any other metal. This could cause a spark, which could ignite the hydrogen inside the battery.
  • Clean the battery. Dirt retains moisture and becomes slightly conductive, especially dirt that is exposed to acid fumes from the battery. The current that flows over the outer surfaces of the battery through the dirt promotes corrosion of the nearby metal.

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