De-ionised water is quite important to your car’s battery. Did you know that lead-acid car batteries are full of water? Lead plates make up the internals of lead-acid batteries, but to facilitate a flow of electricity between the plates, they’re immersed in a solution of water and sulfuric acid.
When a quality battery charger is charging a car battery, it requires a stable ambient temperature to juice up safely, otherwise, it might overcharge. Most modern battery chargers include ambient temperature sensors to adjust the flow of charge depending on the battery’s environment but left to charge on a device that doesn’t offer this capability, and the high flow of current may cause water content to start decomposing.
Once enough water has decomposed, the battery cells will become too acidic, leading to the sulfation of the battery plates and a reduction in performance as a result of poor current flow.
The best de-ionised water for car batteries at a glance:
The best de-ionised water for car batteries: Holts De-Ionised Water – Buy now from Amazon UK
The best all-rounder: CarPlan De-Ionised Water – Buy now from Amazon UK
The most convenient de-ionised water: TRIPLE QX De-Ionised Water – Buy now from euro car parts
Now you might be wondering where you can get your hands on some de-ionised water. Luckily, it’s very easy to find, but we’ve gone ahead and picked out our favourites to make it even easier.
The best de-ionised water
Pros
- Multi-purpose
- Established brand
- Large volume
Cons
- Other options represent better value for money
- Difficult to pour into battery directly from bottle
The best all-rounder
Pros
- Multi-use water
- Large jug
- Good value for money
Cons
- Jug cap too big to pour straight in
- May be slightly difficult to open
The best for de-ionised water for convenience
Pros
- Small bottle for easy pouring
- Easy to store when not in use
- Best seller at euro car parts
Cons
- You may run out quickly
- Other options are more versatile
The best value de-ionised water
Pros
- High purity
- Multi-purpose
- Expert brand
Cons
- Container size overkill
- Recommended use within 12 months
The best for BS EN standards
Pros
- Multi-use – great for detailing as well as batteries
- Double filtered and UV treated
- Compliant with BS EN ISO3696 & BS EN 285
Cons
- Not great value for money
- Difficult to pour into battery directly from bottle
FAQs
Why is de-ionised water used for topping up car batteries?
De-ionised water is free from impurities such as minerals, salts, and ions. Regular tap water contains minerals that can build up inside the battery and reduce its lifespan or performance.
What happens if I use tap water instead of de-ionised water in my car battery?
Using tap water can introduce impurities like calcium, magnesium, and other minerals into the battery. These minerals can cause deposits on the battery plates, leading to reduced battery efficiency, corrosion, and eventually, a shorter battery lifespan.
Can I overfill my car battery with de-ionised water?
Yes, overfilling the battery can cause the electrolyte to overflow when the battery charges, leading to potential damage to the surrounding areas of the battery and the battery itself. It’s important to fill the water only up to the recommended level, which is usually just below the battery cell’s filler neck.
What is the difference between de-ionised water and distilled water for car batteries?
Both de-ionised and distilled water are suitable for car batteries. Distilled water is produced by boiling water and condensing the steam, which removes minerals. De-ionised water, on the other hand, goes through a process that removes ions, including minerals and salts. Either type is free of impurities, making both safe to use for topping up batteries.
Can I use bottled or filtered water instead of de-ionised water for my car battery?
No, bottled or filtered water can still contain minerals and impurities that could damage your battery over time.
Is it necessary to wear protective gear when topping up a car battery with water?
Yes, it is recommended to wear gloves and safety goggles while working with a car battery. The battery contains sulfuric acid, which can be harmful if it comes into contact with your skin or eyes. Always work in a well-ventilated area to avoid exposure to any potentially harmful gases released by the battery.
Topping up your battery’s water content
If your lead-acid battery is indicating low water content – most have a water level indicator – then you’ll need to top it up. When it comes to the source of your car battery water, be advised that simple tap water won’t do. It’s crucially important to fill up your battery with deionized water, as this process purifies the liquid of dissolved minerals and other contaminants. Any impurities or minerals left in the water will interfere with the battery’s chemistry, impeding performance, so pure deionised water is imperative.
Topping up your battery with water is a safe and easy process, though we recommend wearing eye and hand protection to negate the risk of injury. Ensure that your battery is charged up before adding any more water to avoid runaway electrolyte levels, as this may damage your battery.
How to add water to your battery
Begin by opening the water valve caps on your battery to expose the water openings. Once open, you should be able to inspect the water level by looking into each opening – the depth should be around 2cm above the plates for a healthy battery, any lower, and you’ll need to top up.
The method by which you add water to the battery should depend on how much is needed. If the tank is in good shape but could do with a small increase, using a dropper or pipette will allow you to accurately monitor how much is going in while reducing the risk of spillages. If the battery is completely dry, pour from a small bottle to save time.
Remember: overfilling your battery with water can cause electrolyte dilution, leading to a loss of power, while underfilling can cause sulfation, a chemical reaction that will increase charging times and shorten the battery’s life. When filling up your battery with water, it’s important to get it just right for the best results.
Once you’re satisfied with the water level of your battery, you can reapply the valve caps and return the battery to your car’s engine bay.
Seth Walton is a Staff Writer on the Parkers road test desk. His duties include refreshing car review pages with up-to-date testing, reporting on car launches and other industry events both at home and abroad, and the occasional news story when needed.
How we choose
All of these de-ionised water products have been hand-selected by our team of experts who have spent hours investigating and researching de-ionised water products to make it easier for you to find the very best, and we’d never recommend a product we don’t believe in.
Where possible, we also test and share the latest and best products you should know about.
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