To keep your car functioning in top condition it is important to ensure the car battery water level is maintained. A good quality battery usually lasts up to 6 years, but even with the best this is not a guarantee. The life of your battery just like every part of your car depends on how you take care of it. One of the simplest maintenance tasks is to check the car battery water level and topping it up when necessary.
Read our full guide on car batteries.
| What is the water in your car battery?
The liquid in your car battery is electrolyte which is a mix of water and sulfuric acid. The electrolyte is what allows the ions to move between the positive and negative plates of the battery’s cells when the battery is being charged or discharged.
| Safety first!
The liquid in your car battery contains sulfuric acid. Sulfuric acid is very corrosive and can cause harm to your eyes and skin, as well as damage to your car. Whenever maintaining the water in your car battery be sure to wear the appropriate personal protective equipment, such as goggles, gloves and apron. Also, measures should be taken to protect the environment around where you will be working.
| Check your battery isn’t ‘maintenance-free’
Not all car batteries require the water to be checked or refilled. Make sure that your battery can be opened and serviced. Maintenance-free batteries are completely sealed and should never be opened. Batteries that require regular water service often have service instructions and warning labels clearly visible.
To be sure, visit your battery manufacturer’s website for guidance. Strictly follow manufacturer guidelines on how to fill the battery with water.
| Don’t refill your car battery with tap water!
Never use tap water when topping a car battery. Filling with water from the tap could damage it. Tap water contains impurities such as minerals which collect on the plates in the battery’s cells reducing its capacity and usable life.
Professional auto mechanics and car battery manufacturers recommend using pure water such as deionized water or distilled water for filling car batteries.
In case of an emergency and there are no readily available sources for deionized water or distilled water, use rain water instead when possible.
| Adding too much water to your car battery
Too much of a good thing is bad and adding too much water can damage your car battery. When the car battery is charging or being used, the volume of the battery’s electrolyte increases. Over filling the battery causes the electrolyte to overflow out of the battery cells. Electrolyte is corrosive and can cause damage to the battery and surrounding equipment. Also adding too much water can dilute the electrolyte solution resulting in poor battery performance.
If you have experience an electrolyte spill then you can use an liquid spill absorbent powder to help clear it up.
| Don’t refill your battery with acid!
The level of the electrolyte in your battery decreases due to the water being evaporated or from being lost due to a chemical process called electrolysis. As it is water that has been lost, only water should be used to refill it.
If the battery has been overfilled, or electrolyte has spilled out, then the electrolyte will need to be ‘rebalanced’, we suggest using a garage for this task as they will have the equipment and experience to do this in a safe manner.
| Check your car battery water level
To keep your car in prime condition regularly check the car battery water level. This simple tip can save you from costly battery purchases or getting stuck in the middle of nowhere with a dead battery.
| How often should I add water to my car battery?
There is no fixed rule to how often you should check your car battery water level. The suitable frequency will depend on:
- battery age, older batteries tend to require more maintenance.
- quality of the battery, better quality batteries lose water slower then poor quality.
- air temperature, the hotter the ambient temperature the quicker the water loss.
- Usage, most of the water loss will be during charging, so the more starting events the more the battery will be discharged and then charged.
We recommend that you start out with checking your battery at regular intervals, such as weekly and recording this on a calendar. Overtime you will notice a pattern to when you refill the battery, and this will give you the frequency for the future.
So, if you check every week, but only need to add water every sixth week then your watering interval will be every six weeks and you can start to increase the intervals between your inspections. You would need to increase this if the air temperature increases or you start to use your car more often.
If you notice that your battery needs more and more frequent water refills then this can be an indication that there is a problem with the battery, or possibly the charging system. At this point it is worth getting it checked out by a professional mechanic.
| How do I check my car battery water level?
A low electrolyte level will expose the plates of the battery’s cell and cause irreversible damage. It will also reduce the performance of the battery and you may experience starting issues or other related electrical problems.
There are several ways you can check the water level in your car battery:
- External level indicator. Some batteries that require refilling will have a ‘upper level’ and lower level’ visual guide printed on the outside of the battery
- Visual inspection in the individual cells. Remove the ‘caps’ from the cells and make a visual inspection of the water level. When your car battery is fully charged the water level should be level to the bottom of the tube. It is important to make sure the level covers the plates inside the cell.
| Car battery charge and water level
When your car battery is fully charged the water level inside the battery will be at its highest. To know the state of charge of your battery is it worth checking the voltage of the battery. We have a guide on car battery voltage that will help you to better understand the voltage reading and state of charge.
| How do I fill car battery with water?
Steps to filling your car battery with water:
- The battery contains sulfuric acid so follow the correct safety procedures.
- To add water to a car battery you will firstly need to remove the cell vent tops. Your battery will have a total of 6 cells, so you will need to add water to all 6 of them individually.
- Clean away any dirt from the top of the battery, this will prevent it from getting into the cells.
- Inspect the electrolyte level and ensure it is low, see the previous section.
- Ensure you have suitable quality pure water
- Add water to the battery cells that are low. Each battery cell will not require very much water, so you need to add replacement water gradually. Using a ‘eye-dropped’ (pipette), turkey baster or a bottle and funnel. Do not just pure it in as you will overfill the cells. You can also purchase a specific tool for topping up batteries.
- Check the water levels are adequate.
- Clean up any spills.
- Replace the lids.
| Where do I buy car battery maintenance water?
Replacement battery maintenance water needs to be pure and not contain impurities. You can either buy deionized water, or produce it yourself with a purpose-built system
To buy suitable water works relatively costly per liter, but if you only occasionally require refilling your battery then it is an effective way to go. If you choose to buy the water be sure to buy only what is required for your immediate needs. Pure water will ‘leach’ impurities from its surroundings, including the container it is stored in and the air it is exposed to. Overtime this will reduce its purity level, although it would still be preferable to tap water.
Alternatively, you can buy your own deionized water system. There will be a higher upfront cost to this, but much cheaper in the long-term. Having your own system will allow you to produce water on demand, ensuring its quality and removing the need to remember to buy it! Having your own pure water system will also give you a source for other uses, such as refilling your car’s cooling system or even cleaning your car (the low residue levels of pure water is great for cleaning as it doesn’t leave streaks)!