The Shocking Truth About Car Batteries

For most of us it is sitting under the hood, a black cube with a couple of large cables connected to it.  Certainly not as exciting as the engine.  The only time we consider its existence is when it fails to start our car.

These simple black boxes used to come in two sizes, 6 volt and 12 volt.  If you had an English manufactured car you might have to deal with a positive ground electrical system.  By the late 1960’s 12 volt became the world standard as well as negative being the ground to the car’s chassis.


Twelve volts has been sufficient for the automobile industry for decades and the battery design has remained pretty much the same – lead acid.  Yes, dear folks, there is both lead and acid in most car batteries.  It is that chemical reaction between the two that releases the voltage our cars require to turn the engine over and fire the spark plugs.  It was invented in 1859 by Gaston Plante, a French physicist.

But it doesn’t use just volts to turn over the starter.  No, it also uses amps.  That is why CCA (cold cranking amps) is an important consideration when picking a replacement for a worn out battery.  It is a measurement of the amperage that the battery can supply for 30 seconds at zero degrees F.  That is why most battery failures happen in the colder winter months.   Cold weather reduces the battery’s output.  And hot temperatures reduce a battery’s life.  Which leads one to wonder why they are kept in the hot engine compartment.

It is important to understand a little about the chemistry used in the common lead acid battery.   As electricity runs through the battery it causes the water inside the battery to change to its basic elements of oxygen and hydrogen.  I hope you recognise those two elements and their explosive nature. 

Battery Maintenance

Today batteries come in two basic types – sealed and unsealed.  The sealed can be lead acid with the same distilled water mix as the unsealed or they might be the “gel” battery type where it is not only sealed, but there is a gel used instead of a liquid.  The sealed gel batteries don’t need to be vented either.  This can be a plus if you ever decide to move your battery from the engine compartment to the trunk.


Always take time to inspect the battery terminals.  These are either on top of the battery or on the side.  The top ones are posts about an inch in diameter where the cables are held with clamps.  Side posts have threaded spots where the cables bolt up to.  Notice that in both cases each terminal is far apart from each other.  You never want to have anything that can conduct electricity touch the two terminals together.  I’ve seen mechanics foolish enough to be wearing a metal watch band touch the positive terminal to the frame and weld themselves to the frame with the watch band.  One very hot watch band.

Cleaning the battery can be a good thing if it is done the right way.  First off you should disconnect the terminals starting with the negative side first.  If the terminal has a red cover than it is NOT the negative.  Once the battery is disconnected from the electrical system you can clean it carefully.  You should be wearing safety glasses that shield your eyes from any possible splatter.  Remember, there is acid in that battery.  You should also be wearing latex or vinyl gloves to protect your skin.

These batteries weigh anywhere from 40 to 60 pounds.  If you can manage that weight safely then remove the battery from the car.  This will protect the car from any acid splatter that might occur accidentally.

Auto parts stores sell spray-on battery cleaners that make it easy to apply.  Remove the excess cleaner and dirt with paper towels and dispose of them carefully.  You can make your own cleaner with a mix of baking soda and water.  The baking soda neutralizes the acid on the outside of the battery.  Don’t get any on the inside of the battery.

The terminals and clamps should be brushed clean with a small wire brush being careful not to get any of it in your eyes.  That is one of the reasons you are wearing safety glasses.  Auto parts stores sell specially made brushes to clean the terminals and clamps too.

If it is a sealed battery that is as far as you go.  But if your battery has caps covering the cells you can pull or unscrew them and check out the “water” level in each cell.  Clean carefully any new dirt exposed from removing the covers being certain not to get dirt or cleaner into the cells. 


You should use a flash light to view inside each cell.  NEVER use a match or flame!  There is hydrogen gas released and batteries will explode.  A battery explosion can not only damage your car it can kill or maim you while spreading acid over everything.  A flash light is safe though.  As you peer down each cell’s hole their should be “water” covering the lead plates.  If the lead plates get exposed to air it is likely that you are going to be buying a new battery.  You should add only DISTILLED water to a battery if the water is low.  Tap water has too many contaminates to be used.  You should only fill it so that the water acid mix come up to the bottom of the plastic tubes, never to the top of the hole.  Any excess water should be captured with a paper towel.  Then the caps need to be secured.


When attaching the cables back onto the battery be certain that the positive terminal goes on first.  Make certain that you know which terminal is positive, too. It should be marked on the battery case itself.  Attach the negative terminal last.

How long should your battery last?

That’s easy, it depends.  Today’s cars ask a lot out of the 12 volt electrical systems and the battery, too.  They need to run DVD players, GPS units, heated seats, heated cup holders, and hundreds of sensors, no to mention the engine, lights, radio, etc.  As a result car batteries don’t always last for five years or more.  With all the demands on them they are more likely to wear out in two or maybe three years.

Some cars do better than others.  Subaru cars tend to be frugal with their power demands as are many Honda and Toyota cars.  Cadillac, Chevrolet, Nissan and GMC models are are the opposite end of the demand scale.

Soon we may see the twelve volt system disappear and a new standard, the 42 volt system will become the standard.  This will allow plenty of power for the miriad of devices that make up modern cars.

This entry was posted in Automobiles, Car Stuff, Care and Feeding, Cars, Servicing Cars. Bookmark the permalink.

49 Responses to The Shocking Truth About Car Batteries

  1. markitude says:


    Great coverage of the material. Upon reading this, I felt the urge to recount my exploding battery story, grabbed camera and headed outside to take picture of the remains, with the planned intent to link here. Alas, I remembered that I decided that a battery with the top 1/3 of it blown away was a big environmental hazard, leaking acid, lead and all, and had turned it in last year. In any event, let me assure readers who haven’t experienced the realities of a hydrogen explosion caused by arcing cable connections and heat from high current draw trying to start a cold diesel in the middle of winter, that it is spectacular. I had opened the battery cover lid and was reaching in when it went off – it sounded like a 12 gauge shotgun going off, and my hand when flying back past my head and was numb. For a moment, I thought I’d lost it or at least some fingers, but was gratified to see all were still there. I was splattered with acid, and let me just say, that when you wash those clothes, you should expect them to come out of the washer with holes eaten in them. Instant acid washed jeans.

    • Tony Griffey says:

      I too had a battery blow up in my face back in 1980 when my car would not start I had my wife to crank the car and I was going to turn/Twist the cables It made a quick hiss and then BOOM Filled my eyes full and I was lucky, Only came out with one small cut on my left cheek from a flying piece of the casing, Thank God I still have my Vision If that one piece would have been to up 1/2 inch I could have lost an eye. OK One better than that I was out fishing in a boat and had two cans of gas for the boat motor, When one can of gas ran out I was going to switch them out, Just when I turned with the full can of gas I lost my balance and fell sitting the 5 gal, steel can of gas right down on top of the battery And in a split second BOOM Thank God again it did not burn through the bottom of that can of gas, I would not be here today.

  2. Dan Paquette says:


    Your articles are an inspiration for me when I launch my blog again…. only mine will be on fish keeping and wood working.

    I would add that if you have an extra battery sitting around, make sure it is not stored on the ground or on a concrete slab. Placing it on a sturdy shelf or top of an old milk crate would be advised. A car battery left on the ground will naturally discharge at a faster rate. I’d often question this until I experienced it first hand and some college made me smarter about electricity.

    As for keeping them in the trunk… venting certainly is an issue, but I’m sure that longer length cable and extra install process adds cost even if it was done with high volume new cars. (Boss 429 came with it in the trunk!)

    I went looking at some vehicles the other day when I was ordering parts for my truck. Popped the hood on a new Dakota and noticed they had wrapped the battery in insulation…… Must be the signs of the ever shrinking battery compartment.

    Also of note, maybe it is that batteries are now made better, but ten years ago or more I’d be lucky to get 4 years of reliable service out of my car batteries living near the Canadian border. I’ve been getting 5-7 years living in the south even with the heat.

  3. Jim says:

    Dan –

    Be sure to let me know when you start your blog! Thanks for your comments.


  4. Tim Supples says:

    Re: batteries in trunk

    The Holden Commodore (aka forthcoming Pontiac G8) has the battery in the trunk. I assume it will follow over with the G8? They moved it there to help weight distribution. in addition to moving the engine further back in the engine bay. Glad I won’t have to work on that engine!

  5. Gtreat blog, i have a 1996 3000gt with the original battery, i always top up with distilled water every winter and its never let me down (touching wood!)


  6. t says:

    Thanks for the informative article.I wanted to share an article I wrote about car battery boosting with you and your readers. You can find it at:
    The reason I think they are putting the battery in the trunk is mainly for wheight distribution as some of you mentioned, and that has also a negative effect. When you do that the starter and alternators will have to work harder due to the extra load the long positive cable represents.
    There are ways to extend the battery life, one of them is with a solar maintaner, a battery saver, some battery desulfaters seem to work. But the average life is ussually 3 to 4 years for conventional batteries.
    Again Mr. Jim, thanks for the exellent article.
    Pedro Talavera.
    Miami Fl.

  7. milo says:

    very good and very infromative blog..
    easy to understand english. 🙂

  8. Jesse says:

    That business about a battery discharging faster if sitting on the earth or concrete is pure unadulterated wife’s tale baloney!

    The story held a little water eons ago when battery cases were made of wood, instead of hard rubber or plastics.

    Old ‘stories’ die hard.

  9. steve says:

    Great article on a much overlooked part of the auto. I agree, don’t keep your battery on the ground, it will discharge as the earth is a natural ground. Keep the battery clean, as believe it or not dirt, which is earth, does not have to be connected to the ground. Dirt on top of a battery will cause the battery to discharge (not much, but it is measurable). You can measure it w/ a voltmeter.
    Today’s batteries actually don’t have to run anything that they didn’t run in the past. Once the car is started you can throw the battery away (until you need to start it again). The alternator powers the whole system, and gives the battery a little charge to top off what it lost during cranking.

  10. Steve . Where did you find that information about the alternator not needing the battery after the car starts? The alternator can’t make all the power needed when you have all the accesories on. Like ac, defoger, high beams, brake lights, wipers, lowering a window. That is what the battery does, assist when there is too much load.

    I did some research and all battery manufacturers I contacted say batteries don’t drain if left on the floor.
    Most people that say that about batteries draining on the floor also say that in Florida you don’t need a thermostat…

  11. Ron says:

    I have read that sulfide build up on the plates in the battery is what cause the battery to die after a few years. Is it possible to clean it out either with a chemical or just by scraping the plates with a sharp object or a wire brush?

    • Jeff W. says:

      I have flushed a battery clean of all acid, filled it with distilled water, charged it again and repeated the process. Yes, it worked and the battery also worked at least for another 3 years in an old Bronco I used to have that got driven only three or four times a year. When I got the battery it read only ten volts and had quite a bit of build up. I’m getting ready to attempt it on a smaller battery now.

  12. jimsgarage says:

    Ron –

    Let’s face it, lead acid batteries are not meant to last forever. Sulfide build up is part of the electrolysis process that occurs as the battery is charged and discharged.

    I would NOT advise anyone to scrape it off the plates of their car battery. Hopefully most batteries out there are sealed and any others should be treated with the utmost respect as they contain acid and emit the gases hydrogen and oxygen.

    If you don’t have a sealed battery then you should ONLY use distilled water to fill it to the proper level. The proper level is NOT the top of the holes. See the text above for an explanation.

    There are some battery chargers available out there that have a charge/discharge cycle that is designed to remove most of these deposits. Be certain that if you purchase one that you follow the directions carefully. I believe that you must remove the battery from the vehicle prior to using this feature of the charger.

    Do not introduce any chemicals into the battery in the hope of extending its life. Everything has its lifespan and so do lead acid batteries. Distilled water is the only additive to use.

    Remember that the electrical demands of cars sold in the last ten years is many more times as intense as were ever imagined when the 12 volt battery became standard in cars. The days when you could get nearly ten years of useful life out of your vehicle’s battery are long gone. Five is doing well.


  13. Alex says:

    Back in the seventies I worked at a service station with 3 bays. Us second shift gas jockeys did a lot of minor repair and tinkering. One of my fellow amateur mechanics was attempting to charge his three on the tree Econoline, when I heard the explosion. More like a loud pop as the top of the battery blew away. He was ok, but I never forgot it.
    After lottsa cars, and fleet service trucks, you can bank on about five years of battery life at a minimum.

  14. kground says:

    One important point you missed: always make sure the battery is fully charged before adding water ( the exception would be if the plates are exposed – then add just enough wate to cove rthe plates before charging. The liquid in a lead acid battery expands >significantly>>BUT I DO NOT encourage anyone to try either of these methods, as there a myriad of ways things can go wrong and hurt you or pollute the environment.<<<

    Alfa Romeo and Fiat have had the batteries in the trunk since the 50s, mostly I think for weight distribution. The 54-65 Guilia and Guilettas were prone to catch fire in rollover accidents because the battery was right next to the fuel filler neck (which was none to secure back in those days), and the battery would usually come loose, break off the fuel filler neck, and then spark around enough to set the fuel on fire.

  15. kground says:

    … as the solution expands significantly as the battery is charged, since charging moves metal off the plates and into solution.

    There are two main failure modes for a flooded lead-acid battery. Sulfation is mainly a problem with batteries that sit idle for long periods, or those that are allowed to sit discharged. Sulfation causes an increase in internal resistance until eventually you can’t get enough cranking amps to start the engine even though the battery might still read fully charged on a voltmeter or hydrometer. The other failure mode is the shorted cell. As the battery is charged and discharged metal ismoving between the plates and the solution and some bits will tend to fall to the bottom of the cell, especially wiht high rates of charge and discharge. There is some extra room there but eventually themetal builds up enough to short the plates and then that cell is done. (there are six 2V cells in a 12V battery).

  16. kground says:

    With a shorted cell the battery may still be strong enough to start the engine (especially in a warm climate), and the only indication you might have of a shorted cell is a low reading on the voltmeter if your car has a voltmeter. But the alternator will continue to try to pump juice into the battery trying to bring the voltage up to what it would be for a fully charged battery with 6 good cells. With some vehicles (F150 300-6 comes immediately to mind) if you let the situation continue you will be buying an alternator soon.

  17. kground says:

    I once knew a fellow who fixed shorted cells by dumping all of the electrolyte out into a clean (nonmetallic!) container, flushing the battery out with a hose, and then pouring the electrolyte back in. It works sometimes. And I have fixed some moderately sulfated batteries by adding a few drops per cell (no more!) of concentrated Hydrochloric acid. This is sold as concentrated muriatic acid used for washing bricks, and it is nasty stuff. Follow the acid immediately with several deep discharge cycles at at least 30A for a full sized car battery or 5A for a motorcycle battery. If it doesn’t work the first tme don’t bother to add more HCl, that battery is done for.
    >>BUT I DON’T ENCOURAGE anyone to try either of these methods…etc.

  18. jimsgarage says:

    Thanks for including those additional thoughts. For removing sulfates that affect the batteries ability to hold a complete charge – getting a replacement battery is probably the best route for most people. If they know of a shop that has a charger designed to remove sulfates, then let the professionals do it for them.

    The point is that the batteries used in automobiles can be very dangerous if not handled properly. I would not want to see anyone get hurt out there.


  19. autotech says:

    We detail every car that we buy for our small dealership, recently it seems a day after we get our car back from the detailer 90% of our battery’s are going bad, is it possible that the solution can kill the battery I keep checking to see if anything has been left on and there is never anything left on I cant quite figure out whats going on everyone thinks I am crazy but I am starting to think it our detail guy can someone help me

  20. jimsgarage says:

    I would suggest that you disconnect each car’s battery and remove it from the vehicle while the engine compartment is being cleaned and put them back after the engine compartment is done. BMW’s and Miata’s should not be a problem because the battery is in the trunk.

  21. Brian says:

    I enjoyed your article very much. I have heard it suggested that a battery be insulated (thermally) From the heat of the engine compartment, for those not wishing to spend the time/energy/expense to relocate the battery itself.

  22. jimsgarage says:

    Brian –

    I’m glad you found the entry interesting.

    Batteries must live in a pretty rough environment. It is not only the heat and cold but just think of the vibration and g-forces. It might help to insulate the battery from the engine compartment heat, but realize that it will also generate some of its own heat as it is discharging and being charged.

    In some very cold climates people use a heated wrap to keep the battery from freezing when the vehicle is not being used.

    Mazda Miata has its battery in the trunk and the Mitsubishi Evo X also has the factory battery in the trunk. It not only keeps it out of temperature extremes, but it places the weight in a better spot.

    Moving a battery to the rear of a car is something that must be carefully engineered so that a fire hazard isn’t created. A sealed battery should also be used so that dangerous gasses are not creating another hazard.


  23. Noel says:

    I spent a winter in Lake Placid, NY, and night time temps would drop to -30 F. This was back in the day when multi-grade oils didn’t work so well in the air-cooled engine in my old VW Bug so I ran a straight 30-weight oil. But at -30 it was like molasses! With that thick oil, the battery was barely up to cranking the engine in the morning, so I wrapped a heat tape around the battery and plugged it in when I got home each night.

    That gave the battery full power and it cranked the engine every time, no problem.

  24. Kevin Martin says:

    The all important battery bracket.

    While your buying a new battery at the specialist battery place at least, you will find that they have battery brackets at surprisingly low prices.
    The local guy once had sitting in the middle of the new battery rack, a half melted example. On questioning, it was the result of a lad who had purchased the battery and the guy had watched him fit it, without a battery clamp. He offered to sell him one for a handful of dollars and was declined.
    2 months later he was back swearing & cursing because the battery had bounced and shorted on the underside of the bonnet, causing holes to be burnt through, the battery melted sending acid everywhere and the wiring loom to be badly damaged to the extent of needing replacement.
    Not surprisingly, no one accepted liability for faulty battery manufacture etc.
    An expensive lesson.


  25. Kevin says:


  26. Wesco pikes says:

    Can i use still water to toppup my cars battery or is there any other way then distilled water.

    • jimsgarage says:

      I depends how much you care about your battery working. Well water or city water contains impurities that can shorten the life of your battery. Most grocery stores have distilled water for about $1 a gallon.

  27. john says:

    Hey Jim. I’m a land rover owner. I have a question about the size battery needed in a truck or car. Here is my Q; If a automobile requires a 600 AMP min, battery and you install a 500 AMP battery… What most generally will happen to an Alternator?

  28. Brian says:

    The short answer is that your alternator will likely experience a shorter life span. There are many variables involved. I found much information from an online article-

  29. Pingback: Ka-BOOM!! So a car battery really CAN explode?! | Grains of Sand

  30. mel says:

    what will happen if battery water spreading on my car compartment and what is remedies.

    • jimsgarage says:

      Since the battery “water” contains acid it can do bad things to metal and paint. First off you need to find out why you have the “leak” and fix it. Make sure you have protective gloves (laytex, vinyl, etc.) and remove the battery fluid with paper towels and be sure to dispose of them properly. To neutralize the acid you can mix baking soda and a little water and use the mix to wash the area. A leaking battery is nothing to ignore. Fix the problem. Take it to a professional as soon as possible.

    • Brian says:

      First and immediately, put baking soda on any and all areas which the “battery water” has contacted. It contains sulfuric acid and is very dangerous to both people and whatever it contacts (with the possible exception of some plastics). Wherever possible, remove anything which has been subjected to the battery acid and rinse it thoroughly with a mixture of water and baking soda (use generous amounts of baking soda to help neutralize the acid). Only after these steps should you attempt to remove battery or further investigate the reason for the loss of “battery water”. Use both eye and hand protection, as well as protection for anything which could possibly come into contact with the highly corrosive battery acid. Do not breathe any fumes which may be present. There is much more information on safe battery handling and related battery subjects in an article online at Please let us know if you find this information helpful.

  31. Patrick says:

    I have found a corroding battery from 1950’s maybe in the ground in my garden. What should I do with it?????

    • jimsgarage says:

      First put it in the oven at 350 degrees… HA! No DON”T DO THAT! I’m just kidding. See if a local auto parts store will take it or maybe you are fortunate enough to have a town that offers dangerous materials disposal.

  32. bill says:

    I don’t think there are any unsealed batteries sold anymore and all new batteries now have polypropylene cases and can safely be stored on a concrete floor unlike the old days. I am in auto parts and was told this by a battery manufacturer rep.

    • Bil says:

      It’s an absolute fallacy that any battery stored on a concrete floor will be damaged. And for those that want to restore their battery, just make sure you wear protective goggles and when needed gloves also. For batteries with sulfated plates many people have dumped the acid from each cell and replaced the fluid with distilled water and Epsom Salts. Other have simply added the ES to the existing fluid instead and had success. There’s even a fix for car batteries with shorted cells. Do not do any of this without good instructions. The old acid must be neutralized (easy).

  33. Alan says:

    I wanted to see if anyone can shed some light on what happened in my garage last night. I have five marine batteries and a few motorcycle batteries that I keep on the work bench. I rotate a few trickle chargers on them thru the winter months and have used that same spot for years so there has been spills ect…ect…. I just relocated them five feet down the bench to the left two weeks ago. Above the bench I have some kitchen cabinet uppers mounted and on the face of the cabinet I have had 12-15 sheets of copy paper stuck thru a nail for a little over a year now. Directly under the paper I have two types of razor blades in the 100 pack attached to the face of the cabinet. One type is the regular type for a box cutter and the other are the thinner type you slide into a scraper made of carbon steel and aluminum. I bought a cordless drill last night and plugged it in on the bench under the paper where all the batteries used to be. An hour later I smelled smoke and when I went out to the garage the papers on the front of the cabinet were completely engulfed in flames. Has anyone ever heard of such a thing or do I have an arsonist on my street

    I would appreciate any feedback Thank you

  34. Marshall Singer says:

    Very well written article, Great job !

  35. I know this is an older post. But why is this a “shocking” truth? I didn’t see anything shocking about any of it. Trying to get views maybe?

  36. Terry says:

    Good article, but I can’t agree with your statement that accessories like DVDs and GPS etc affecting battery life. Their current draw is tiny compared to cranking a cold engine,
    and modern alternators produce more than enough to cancel this when the engine is running, and quicly replace the discharge if they have been used with the engine off.

  37. Amanda Pretty says:

    Hi Jim, I’m hoping you can help, I’m using my old battery to hold solar power in my van. If put it in a plastic box with a plastic lid and when the lid clamps shut the lid is pressed against both terminals. Is this safe?

  38. jimsgarage says:

    The fact that the lid presses against the terminals is not too bad, as long as they don’t chafe through some time in the future, but the larger problem is the release of combustible gasses from the battery being trapped inside the box. Keep in mind that these batteries give off oxygen and hydrogen so if not vented they will produce an explosive mixture. Look up the standards for venting racing battery boxes to get an idea of what should be done. Also, be certain that the battery is mounted securely and doesn’t have a chance to get loose, especially in an accident. Be careful.

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