Do You Need Distilled Water for a Battery?


Water Used by a Battery

A car battery delivers power to start a car. The battery usually has internal plates that make the battery work. These plates are covered with water. During battery activity, some of the water through chemical action breaks down into hydrogen and oxygen gases that may evaporate from the battery. When this happens the water level drops and the plates are no longer covered with water. They do not operate efficiently and are damaged. In many batteries, water can be added regularly to ensure the plates are covered. Most battery makers recommend adding distilled water to these batteries to bring water to the correct level so that the battery works properly.

Checking the Battery


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Modern car batteries are often maintenance-free. They are sealed and do not vent hydrogen and oxygen gas. They do not have removable caps. These batteries sometimes have a green "eye" on the battery that turns black when the battery needs replacement. These batteries need no water added. Other batteries have square caps that can be carefully removed with a flat blade screwdriver. Under the caps are plastic filler holes that lead to the battery plates. If the battery plates are exposed to air, distilled water should be added to each hole to cover the plates. Use a filler syringe to slowly add water. Do not fill to the top of the tubes. Gently and firmly put the caps back in place.

Why Use Distilled Water

Many mechanics and car owners use tap water to top off the battery. This can lower performance and shorten battery life due to water impurities that upset the normal battery function. Battery manufacturers recommend distilled water for better performance and longer battery life. Distilled water is water from which salts and minerals have been removed. Water from faucets, lakes and wells usually has dissolved minerals and salts. These minerals and salts affect the chemical action in the battery. The battery works harder to maintain its charge and does not operate as efficiently. When the battery works harder, its internal temperature may get hotter while the battery is working. This causes more evaporation and requires more water. Distilled water ensures the correct battery chemical properties are maintained.

Where to Get Distilled Water

Distilled water is available at most supermarkets and merchandise stores. Check the bottled water section. Distilled water is easy to find because it is also used in steam irons. Many automotive stores carry distilled water because some car owners use it in their car coolant systems.

Safety Tips

Follow owner manual instructions on battery maintenance. Always wear safety glasses before removing battery caps. Do not smoke around batteries as the escaping gases may be explosive. Wear gloves when removing and replacing battery filler caps. Do not get battery fluid on hands, face or clothing as battery fluid is acidic and corrosive. Flush exposed skin immediately with lots of lukewarm water.