What Causes a Battery Boil Over?

by Casey Case
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Jessica Isaac/Demand Media

If you have ever seen acid coming out of the top of your car, golf cart, or boat battery, you have experienced battery boil over. Boil over can quickly ruin a battery and at best decreases the battery's life. Battery boil is also dangerous and you should know what causes batteries to boil over and how to prevent it.


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Batteries use a water and acid mixture that produces a chemical reaction and results in the charge necessary to start your car, boat or other vehicle. Many batteries need to have water added on a periodic basis to keep this chemical reaction going inside the battery. If you have a battery that needs water added to it periodically, follow the manufacturer's instructions on the fill level. Adding too much water will cause the battery to boil over.


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An alternator that is overcharging the battery can cause boil over. The alternator in a vehicle continuously charges the battery while you drive. The optimum charging voltage for a battery is 14 volts. If the charge gets above 14.5 volts, your battery will overheat and boil, causing severe damage to your battery and eventually making it unsafe for use.


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Recharging the battery with an external charger can cause it to overheat and boil over if the charger is defective or if you charge the battery too long. A defective charger might have an unregulated flow of electricity or it might charge the battery too quickly.


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In order to prevent boil over from occurring, make sure you do not overfill the battery with water. Also, use battery chargers that have regulated flow and do not charge at a rapid rate. Once you are charging the battery, monitor the process to ensure you remove the charger as soon as the battery has a full charge.


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Do not ever try to handle a battery that is boiling over. Boil over spills acid that can be harmful to humans. Also, if you have a battery that boils over, replace it as soon as you can to avoid exposure to acid.

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