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exploded battery
Caution: Sparks can cause a battery to explode!


by Larry Carley copyright
WARNING: Batteries can explode! When a battery charges, it gives off hydrogen gas. Hydrogen is flammable and can explode if a spark occurs near the battery (as when connecting a jumper cable, see safe jump start procedure below).

DO NOT smoke around a battery, or use anything that produces an open flame or spark. The photo below shows what can happen to a battery when a spark causes it to explode.

DO NOT attempt to jump start or recharge a frozen battery. Remove the battery from the vehicle, bring it into a warm room and let it thaw before charging or testing.

Always wear safety glasses when jump starting a battery (to protect your eyes), and gloves when handling a battery (to protect your hands).

According to PREVENT BLINDNESS AMERICA, in 2003 nearly 6,000 motorists suffered serious eye injuries from working around car batteries.

Follow the manufacturer's instructions for testing, jumping, installing, discharging, charging, equalizing and maintaining batteries.

Handle Car batteries With Care

WARNING: Automotive lead-acid batteries contain sulfuric acid in the electrolyte. The acid inside the battery is highly corrosive and can burn your skin if it leaks out of the battery and gets on your skin. This is NOT a danger if the battery is a "gel" or AGM type that does not contain liquid acid. But it can be a concern if the battery contains liquid acid and has removable caps on top. Sealed top batteries should contain the liquid as long as the battery remains in an upright position (do NOT turn it sideways or upside down). Acid may leak out if the battery case is cracked or damaged, so handle with care.

New car batteries come pre-filled with acid, so it is not necessary to add acid to the battery. But most motorcycle and garden tractor batteries are sold dry so acid must be added to each of the cells. Always wear rubber gloves and eye protection when handling acid and pouring the acid into the battery to prevent burns and eye injury.

BCI Warning Label

car battery exploded view
The electrolyte inside a wet cell car battery contains corrosive sulfuric acid
that can spill if the case is cracked or the battery is upset.


Overcharging a wet cell lead-acid battery can produce toxic and corrosive hydrogen sulfide gas. Hydrogen sulfide gas has a strong rotten egg odor. It can cause health symptoms in concentrations as small as 2 to 5 ppm, and can be toxic in concentrations of 50 to 100 ppm. It can also be lethal if the gas reaches sufficient concentration (500 to 700 ppm) inside an enclosed passenger compartment (windows closed, and A/C off or in recirc mode). See OSHA exposure limits for hydrogen sulfide.

The main concern is with lead-acid or AGM car batteries that are mounted inside the passenger compartment or trunk. This includes many late model European vehicles as well as some Buicks and the auxiliary 12-volt battery in many hybrid models.

Normally, AGM batteries do not vent any gas - unless they are being overcharged. If pressure builds up inside a "sealed" AGM battery, it will eventually be released through a safety release valve. Ordinary wet cell lead-acid batteries do produce hydrogen gas when charging and can produce hydrogen sulfide if overcharged. Because of this, an AGM battery inside a passenger compartment should NEVER be replaced with a conventional battery.

For passenger safety, any battery located inside a vehicle must be enclosed in a sealed box that is vented outside the vehicle. This is not necessary with batteries mounted in the engine compartment because any hydrogen has or hydrogen sulfide that escapes from the battery will dissipate and have no direct path into the passenger compartment.


Ordinary 12V car batteries only produce 12 volts, so there is NO danger of being shocked. However, batteries can produce hundreds of amps, so never touch a metal object such as a wrench between the positive and negative battery posts to see if the battery will spark. It will, and produce a current similar to a welding arc that may damage the tool, the battery and/or cause the battery to explode!

HYBRID BATTERY WARNING: On hybrid electric vehicles such as the Toyota Prius, Lexus RX400H, Honda Insight, Ford Escape hybrid, etc., the hybrid battery pack in the back of the vehicle is a HIGH VOLTAGE (300+ volts!) battery. Three hundred plus volts is enough to shock you or kill you, so NEVER work on the hybrid electrical system on one of these vehicles without first disabling or disconnecting the high voltage battery per the vehicle manufacturer's instructions. This must be done with insulated tools and gloves. The high voltage wiring is usually color-coded ORANGE.

battery jump start procedure

Safe Battery Jump Start Procedure

If a battery is dead or too low to crank the engine, you can jump start it using a pair of jumper cables to connect the low/dead battery to a good battery in another vehicle.

Pull the other vehicle as close as possible to the one with the dead/low battery, but DO NOT allow the vehicles to touch. Open the hood on both vehicles, and shut OFF the engine in the other vehicle.

Jumper cables are color coded, RED for POSITIVE (+) and BLACK for NEGATIVE (-). DO NOT mix up the cables or allow the metal ends to touch together because this may damage the battery, charging system and/or electronics on a vehicle.

To jump start the battery, proceed as follows:

1. Connect one end of the RED jumper cable to the POSITIVE (+)post on the dead battery. The POSITIVE battery post will be slightly larger than the NEGATIVE post, and will be marked with a PLUS (+) sign. There may also be a RED plastic protective cover over the positive bttery post.

2. Connect the other end of the RED jumper cable to the POSITIVE (+) post on the good battery.

3. Connect one end of the BLACK jumper cable to the NEGATIVE (-) post on the good battery.

4. Connect the other end of the BLACK jumper cable to a heavy metal ground on the engine or frame of the vehicle with the dead battery. DO NOT make the final jumper connection to the NEGATIVE (-) post on the battery itself because it usually sparks and may ignite hydrogen fumes in the dead battery causing it to explode.

NOTE: On some vehicles the battery is not easily accessible (because it is located inside a fender panel, trunk, etc.), so there may be special jumper connections in the engine compartment for jump starting the vehicle.

CAUTION: DO NOT lean directly over the battery while making jumper connections (in case of explosion).

5. Start the vehicle with the good battery, and run the engine at a fast idle (1200 to 1500 rpm)for a couple of minutes. This will help charge up the low battery and make starting easier.

6. Now you can start the vehicle with the dead battery. If it does not crank or cranks very slowly, wiggle the jumper connections to make sure they are making good contact. Then try again. The engine should start if there are no other problems (such as a bad starter or ignition circuit problem).

7. As soon as the engine starts, disconnect both jumper cables. Do not allow the metal ends of the jumper cables to touch each other or the RED cables to touch anything metal on either car.

8. Keep the engine running 20 to 30 minutes, or drive the car to recharge the battery. During this time, leave the lights, heater, A/C and other electrical accessories off so all of the charging system's output can go into the battery.

NOTE: If the engine dies shortly after it has been jump started, or as soon as the jumper cables are disconnected, it probably means the charging system is not working (bad alternator, voltage regulator, wiring problem or loose/dirty battery cables).

If the vehicle runs okay and the battery charges up, you should clean and tighten both battery cables after shutting the engine off. The battery and charging system should also be tested to make sure both are working properly.

Battery Cautions When Making Repairs:

It is usually a good idea to disconnect the battery before doing electrical repairs. Disconnect the negative battery cable from the battery. This will prevent accidental damage to onboard electronics or wiring if you accidentally cross up the wrong wires or short out a live circuit.

WARNING: NEVER disconnect a battery when the ignition is ON, or while the engine is idling or running.
Doing so can damage electrical and electronic components.

battery terminals

Warning: Disconnecting the battery may cause electronic modules to forget information.

CAUTION: DISCONNECTING THE BATTERY ON SOME LATE MODEL VEHICLES MAY CAUSE DRIVEABILITY OR OTHER PROBLEMS: When the battery is disconnected, power to the PCM and other onboard modules is lost. This can cause a loss of Keep Alive Memory settings. In effect, this "resets" the PCM back to its base settings, so the engine may not run properly until the PCM adaptive memory can relearn these settings. The same goes for the transmission. It may not shift properly or feel the same until the PCM or TCM has had time to relearn the shift adjustments. This may take 10 to 50 miles of driving. Read This BEFORE you disconnect or replace a battery on a late model vehicle.

Disconnecting the battery may also cause other system modules to forget their learned or programmed settings. This includes modules that control the air conditioner, sunroof, power windows, power seats, radio, even some anti-theft or keyless entry systems. Some of these modules may not work properly when the battery is reconnected, or they may remain in standby mode until a special scan tool relearn procedure is performed (which may require a trip to the car dealer for repairs!). So always check your owners manual for any precautions about disconnecting the battery before you remove either cable.

If you are uncertain that disconnecting the battery on your car may cause problems, attach a backup battery, battery charger or Memory Saver" device to the battery cables or the 12 volt power outlet or cigarette lighter BEFORE you disconnect the main battery. If using a Memory Saver (small 9 volt battery), make sure the outlet you plug it into is ON when the ignition is off. Some require turning the key to the Accessory (ACC) position first. Also, leave the doors and truck closed because the interior lights will quickly drain all the voltage from a small 9v battery. You need that extra voltage for the various module Keep Alive Memory settings.

NEVER reverse battery polarity. This may damage the battery, charging system, electrical components or onboard electronics. Except for some antique vehicles, all modern vehicles have a NEGATIVE ground. The NEGATIVE battery post is marked with a minus (-) sign, while the POSITIVE battery post is marked with a plus (+) sign.

Finally, when installing a new battery, make sure the battery is fully charged before the vehicle is driven. This will reduce the strain on the charging system.

brake squeal More Battery & Charging System Articles:

Battery FAQs

Battery Disconnect Problems (Read This BEFORE Disconnecting or Replacing Your Battery)

Battery Testing

Diagnosing A Battery That Runs Down

Hybrid Safety Hazards

Troubleshooting electrical problems

Starting & Charging System Troubleshooting

Starter Diagnosis

Charging System Checks (alternator testing)

High Output Alternators (Why You May Need One)

More on Starters

What You Should Know About Rebuilt Alternators, Starters & Other Parts

Car Won't Start (Possible Causes & Quick Checks)

Diagnosing An Engine that Won't Crank or Start

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