How to water a lead acid battery

Posted by Andy Hill on

A person watering a lead acid battery

Lead acid batteries are one of the most reliable forms of energy storage on the planet. They’re pretty easy to look after and keep performing to their maximum potential. One of the most important factors to consider when is comes to lead acid battery maintenance is lead acid battery watering levels. Keeping the battery water at the correct level means that you will have to water your battery regularly. Putting too much water in the cells and conversely not watering them often enough can both damage your battery. To make sure your lead acid battery keeps running smoothly at all times we’ve put together these simple lead acid battery watering guidelines.



Safety should always be first, so make sure you wear personal protection equipment such as protective eyewear and gloves when working on batteries. The two most common lead acid batteries are flooded, which require regular watering servicing and VRLA which deliver maintenance-free operation. Make sure you check the information on the battery if you’re unsure of which battery you have. The warning labels on your battery should direct you to “DO NOT OPEN” the battery, or “KEEP VENT CAPS TIGHT FOLLOWING WATERING SERVICE.”  It’s vitally important that you follow the warning label instructions. If you have a flooded lead acid battery then a battery watering system or battery watering gun will allow you to quickly and safely water your battery.



Flooded lead acid batteries contain a liquid called electrolyte which is a mixture of sulfuric acid and water. The plates in a lead battery contain an active material that should be continuously bathed in electrolytes while oxygen and hydrogen gas are released during charging. A battery should only ever be filled after it has been completely charged.

Before charging, check to make sure there is just enough water to cover any exposed plates. After charging, add enough water to bring the level to the bottom of the vent, about ¾ below the top of the cell. If you are using a battery watering system, sometimes called a battery filling system, this will automatically fill to the correct level. You can automate the checking process by using an electrolyte indicator which will give you a visual indication of when a battery needs to be filled.

It’s important to note that you should never add sulfuric acid to a lead acid battery.  During normal operation batteries will only consume water, not sulfuric acid.  When your battery’s water level is low, filling the battery with deionized water will keep the battery performing at its maximum. 



While a battery is charging, the electrolyte solution will increase in density. If water was added before charging, the electrolyte levels will expand and cause the battery to overflow. These overflow can damage the battery, cause injury and result in expensive clean-up operations. Adding too much water to a lead acid battery can also result in the dilution of the electrolyte, resulting in reduced battery performance. Using an electrolyte indicator will prevent all of this from happening by showing you exactly when a battery needs water. If you’re not using a lead acid battery watering system, sometimes accidents can happen and if they do there are battery tray monitors and electrolyte removal pumps available. The tray monitor will indicate if there is any electrolyte at the bottom of the battery tray and the electrolyte removal pump makes it easy to get rid of the electrolyte that has spilt over.



How often you need to add water to a lead acid battery will depend on how often it’s used. A marine, or golf cart battery that is only used on the weekends may only require watering once a month. A forklift that’s used every day, may need to have its battery watered once a week. The ambient temperature also affects how often a battery will need filling, as when it’s warm the battery will need watering more often. It’s important to check a battery’s fluid level regularly, an electrolyte indicator will make the checks really easy to carry out.



When filling a lead acid battery, tap water shouldn’t be used. Tap water contains minerals and micro particulates that are harmful to batteries, more so in water softened by water softeners that contain chlorides. Filling your batteries using distilled water is a much smarter investment than a new battery more often than required. There are water deioniser systems available that allow you to create your own distilled water on site.

After filling, the water will sit on top of the acid solution in the battery until it is mixed during the charge cycle. If you need to take a hydrometer reading of the electrolyte, you’ll get more accurate readings after charging is complete.

So that’s it really. Don’t let your batteries get dehydrated, water them when they need watering especially during hot months and you will have a battery that will perform to it’s maximum day in day out.

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  • Good advice

    Joe njoroge on

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