Battery "boiling" occurs when you overcharge a wet-cell, lead-acid battery. Heat causes the liquid inside the battery to change into a poisonous gas. Pressure and heat build up and can cause the battery to catch on fire, or even explode. Since batteries are filled with toxic substances, such as lead, you don't want these types of accidents to occur. The way to prevent boiling is to make sure you don't overcharge a battery.
Check the battery's fluid level. Before charging the battery, pry off its cap with a screwdriver and inspect the battery's wells. Add distilled water to any wells that are dry or low on water. Tap water can cause mineral deposits to form inside a battery, so only use distilled water to replenish the fluid levels.
Examine the battery charger. Ensure that your unit is approved for the type of battery you want to charge. Most wet-cell, lead-acid batteries are 12 volts, and the charge on a 12-volt battery should never exceed 14 volts.
Read the charger's instructions. Some chargers contain a computer chip that automatically shuts off the unit when a battery is fully charged. Other models continue to charge as long as the unit is on. Review the instructions for your particular charger to ascertain whether you'll have to manually turn off your charger.
Charge the battery. Check it periodically as it's charging. Most chargers have a gauge that indicates the charge level. Alternatively, you can use a multimeter to check the battery's voltage.
