Battery Repair School.

          Thank you for your interest in this information. This will save you a LOT of money over the coming years. It is very important to me that this information helps you save money.  If you get into this project and decide it is just not for you, I will be happy to allow you to use the cost of Battery School to go toward  the repair of your battery by us here. Please read all this material before attempting the repair. The more you know, the better you will understand what is going on and what you are actually doing during the repair.

    However, I really think it will be worth your while to learn how to do this. There are likely many rechargeable devices in your home including shavers, lawn tools, entertainment devices. There may be even more in the years to come. I am going to go about this just like you are an elementary student who knows nothing about batteries or electricity. Please don’t feel insulted if I say things that seem very simple to you.   


   Any battery can be dangerous in the right situation. Although problems are rare, you should always wear safety glasses when working with batteries. It is better to be safe than sorry. Be sure to read the notice in each section and heed the warnings.

  When thinking about electricity, it is very much like water. A rechargeable battery is like a little tank. You fill it up with electricity (electrons), put it the device your are using and proceed to let it empty out. When it is empty, you must fill it up again. 

   The battery packs like the ones that come on Dewalt  and other portable tools, are made up of several little batteries. Each battery is about 1.25 volts and is called a CELL. Each cell has a POSITIVE (+) terminal and a NEGATIVE (-) terminal. (remember that).

  The amount of total voltage from a battery PACK depends on how many of these smaller batteries or cells are contained in the battery pack. Tool battery voltage varies from 7.2 volts to 24 volts. When these small 1.25 volt cells are connected in SERIES, the total voltage available depends on how many cells are hooked together. SERIES means the + or POSITIVE side of a battery is hooked to the – or NEGATIVE side of the next battery and so on and so on. The – side of the last battery in the series becomes the or negative side of the entire battery pack. The + side of the last battery on the other end, becomes the + or positive side of entire pack. The over all voltage of the pack, will vary depending on whether the pack has just been recharged or is needs to be recharged.

    All batteries are rated 2 ways. The first is VOLTAGE. The second is MILI-AMP hours (or in larger batteries like in cars, AMP hours). If you go back to thinking about water and do a comparison, the voltage in a battery is like the pressure of the water. Milliamp hours in a battery is like the size of the tank of water.  The more milliamp hours the longer a battery will last in a given application.  A 1.25 volt battery rated at 2000 milliamp hours, would last twice as long as a 1.25 volt battery rated at 1000 milliamp hours. 

     There is one other thing to think about when dealing with electricity. That is current. Current is the amount of electricity or electrons flowing through a device. Current flowing out of a battery is like the amount of water flowing out of a tank. The more current that is flowing out of it, the faster it will “drain” out. 

     Many people do not realize that current is what kills a person when they are electrocuted , , not voltage. It only takes 100 milliamps of current (of flow) to kill a person. An average 1.25 or 1.5 volt cell can put out 10 times that much current or more. A car battery can put out many HUNDREDS of amps. But if you touch both sides of a 1.25 or 1.5 volt cell, or a car battery you will not get shocked. That is because there is not enough voltage (pressure) to force that current through your body.

    When you walk across the room and touch something and get a shock, that is easily over 1000 volts. You are not killed because even though there is a lot of voltage (pressure) there is not enough current (flow) available to actually hurt you. The big power lines going down the road have lots of voltage and current and can “fry” you literally if you were to touch them. 

     Now that you know a little more about how electricity and batteries work, it is time to repair your battery pack. There are several ways to repair these battery packs.

    The first way is very simple and takes only a few seconds. It will take you more time to get set up than to repair the battery.

     The second way is a little more complicated, but sometimes is necessary if the first way does not work. Always use the first method first and if it does not work out, you may need to use the second way to do the repair. Here is why battery packs go bad.

        As a battery pack gets older, one or more of the little 1.25 batteries within the pack (cells) will go bad. Most often the cell will “short” which means that the voltage coming out of that cell will be zero volts (pressure) however even though it is shorted, it will allow the current (flow) from the other cells in the pack to go through it because they are all in series. The current that goes through one cell goes through all the cells..

       If one cell goes bad by shorting, you may not even notice the difference in the amount of power (especially on the 18 to 24 volt packs). That's because each cell is only 1.25 volts. In a 18 or 24 volt pack, that is only a small reduction in voltage (pressure). However, as more and more of them go bad, the tool will not run as fast and will not hold a charge as long. 

    The whole idea of this project is to BLOW those little shorts out of the 1.25 cells that are bad. If it works, the battery is repaired and can be used again. If not enough shorts can be removed to get the pack going again, you may have to replace the bad cells. 

    There are several different ways to fix a battery pack. If you can not fix it the easy way, you will need a multimeter, soldering iron and solder, diagonal cutters, and a screw driver that fits the screws on the battery pack. 

  FIX #1 There are actually 2 versions for FIX #1. 

   The first way is to repair the whole battery at once. This is done by charging the battery for at least 30 minutes. Then remove the battery from the charger and short the battery pack terminals together for 1 to 2 seconds with a piece of 12 gauge wire. Since there is no "resistance" to limit the flow of "current", high current goes through all the cells in the battery at once and often "BLOWS" out the little shorts within the bad cells.

  Once you performed that step, put the battery in the charger again and attempt to charge it. Once charged, you should notice much better performance. It is best to have a voltmeter to help you determine the results you are having, but it is not absolutely necessary. 

         If you want to get a volt meter, you can find one at Radio Shack or on Ebay for just a few dollars. I just bought a new digital multimeter on Ebay for $8 with shipping. That is pretty amazing to me since the first one I ever bought was a couple hundred dollars.  It is a VERY handy device to have around the house so you may want to think about getting one anyway. 

     When a battery pack is fully repaired, the voltage measured across the terminals of the battery pack should be about 10% higher than the rated voltage of the battery pack. Some times a few of the cells will be repaired and 1 or 2 may not. In that case, the voltage will never go to the highest amount, but it may work good enough to satisfy you. 

      The SECOND part of FIX 1 is to use a higher voltage battery in parallel or series (depending on the voltage of the pack) across the battery pack terminals. On a 6 or 7.2 volt battery, a 12 volt auto battery works fine. In this case you place the battery in PARALLEL across the battery pack terminals. Here is what happens. 

    On those battery packs you FORCE a higher voltage and higher current through each cell in the pack. This high current usually blows out the shorts in the cells that are bad. 

   On those 18 to 24 volt packs, the battery voltage would have to be at least twice the voltage of the pack. To have a chance of working you would need to use 36 volts which is 3 auto batteries in series. (remember what series is). This can get a little "hairy" as when working with this higher voltage things can get a little dangerous . (higher voltage and higher current). I DO NOT recommend this fix for higher voltage battery packs unless you have experience with electricity and know what harm it can do to you if you are not careful. (fire, shock, explosion, etc.)

 There is another way to use a 12 volt battery to fix these higher voltage batteries. Remember above I told you to momentarily short the terminals of a fully charged battery together to blow the shorts out of the cells. Then you were to charge it again to see how much better it was. Sometimes there is just not enough current available in a bad battery to do this. 

   However, you can take your 12 volt battery and hook it in SERIES with your battery pack. Hook the POSITIVE of the 12 volt battery to the NEGATIVE of your battery pack. 

     Then momentarily touch the NEGATIVE of your 12 volt battery to the POSITIVE of your battery pack. Here is what happens. 

   Remember you learned that when you hook batteries in SERIES the voltage of the batteries is added together. In this case you are adding the voltage of the 12 volt battery to what ever voltage is left in your bad battery pack. Since there is almost no resistance, a lot of current flows through the battery pack and BLOWS the shorts out of the bad cells. DO NOT leave the wires hooked up as a lot of current is flowing and a MELT DOWN of your wires and other things can occur. You may want to touch the wires several quick times for several short bursts of current. 

 FIX #2     Most of the shorts within the individual 1.25 volt cells can be repaired by forcing enough current through that cell to “blow” out the short. That is done by taking a battery with higher voltage of 6 or 12 volts and momentarily (less than one second) placing it in parallel with the bad 1.25 volts cell. Parallel in this case means hooking the +  side of the battery to the plus side of the cell and the - side of the battery to the minus side of the cell. 9 volt batteries used in radios and other devices will not work because they do not have enough current (flow) available to blow out the short. An automotive battery works very well as it has more than enough current available to do the job.

     Remember I said before that the 1.25 volt cells in battery packs are placed in SERIES. Series means that the plus of one battery is hooked to the minus of the next battery. When hooking batteries in parallel, you hook the positive of one battery to the positive of the other battery and the negative of one battery to the negative of the other battery. (just like when you jump start a car). 

    Here is what happens. Remember that the individual cell within the battery pack that is not working is usually shorted. When you hook the 6 or 12 volt battery across the plus and minus terminals of the shorted cell, a lot of current flows because there is nothing to stop it but the “resistance” of the wires you are using. That high current flow often will remove or “blow out” the internal short in the battery and allow it to work again. (most of the time, but not always.)

 WARNING. Only touch the wires from the 6 or 12 volt battery to the 1.25 volt cell for a short time. (less than one second) Also be aware that because of the high current, one wire could actually spot weld itself to the other battery and would have to be pulled off quickly. (sometimes I touch the second wire to the battery several times for a brief moment, kind of like Morris code. This often takes the short out of stubborn cells that do not fix the first time you pulse them with high current.)

    If you are not sure which battery(s) is bad, and you do have or do not want to purchase a volt meter, soldering iron, etc. you can just use the technique above for each cell in the pack. This will usually fix most of the bad cells.

    To get started, disassemble the battery pack. Different packs are assembled different ways. Most packs are thankfully screwed together. Some are glued which makes it harder to get them apart but not impossible. You must decide if you want to force them apart. Some are almost impossible to disassemble. Others may have potting compound poured around the individual cells which makes the job even harder or impossible. The cells in rechargeable razors and other household devices are usually just laying in there when you take it apart. In the future, you will have to look at each situation to see if the pack can be repaired or not. I figure it is always worth a try depending on the cost of new.

     The idea is to expose the individual cells so you can test to see which ones are bad. If you intend to repair them using the short removal method described above, you can actually parallel your 6 or 12 volt battery to each cell within the pack. You will know the ones that are shorted, because you will get more of a spark. The best way however is to use a volt meter to see which ones are bad.

    If you get NO spark at all, the cell may be open and must be replaced. (If the cell is open, current from the rest of the cells in series can not flow through it so the pack will be DEAD and not be able to be recharged at all. ) 

  The cells that are bad will have no voltage output when measured. It would be a good idea to charge the pack for 15 minutes before taking it apart to make sure the good cells have some voltage output. Put your meter on DC volts to make your test and then test and mark each bad cell with a pen or marker so you remember which ones are bad.  NOTE which end of the cells are NEGATIVE and which ones are POSITIVE and remember that. 

These are photos of a new cell. The left photo is the POSITIVE end and the right photo is the NEGATIVE END.

Usually the NEGATIVE end of the battery will show the most metal surface. The POSITIVE end will be closed in more with insulating material

    Here's something else to consider. Although is does not happen often, a battery can go bad by being “open” rather than “shorted”. Open means that no current will flow through it. If only one cell is open, the battery pack will be dead and will not charge at all. When you take the pack apart, any cells that are not open may still have some voltage output. Even a couple tenths of a volt is ok if most of the other ones have the same voltage. You will not be able to repair an open cell. It will have to be replaced.

NOTE: If a cell is open, and you are desperate to get your pack going again without replacing the cell, you can always solder a jumper wire from the negative to the positive side of that one cell the bypass it. 

 Cells tend to short when the pack is allowed to discharge too far. Try not to let this happen and your packs will last longer. Also charge your packs at least once a month to keep them from discharging by themselves.

 You may also want to replace the individual cells. Go through a pack and mark the ones that have no voltage at all. If you try the short removal method above and have no success, you will have to replace the bad cells. If you have just 1 or 2 on the higher voltage packs, you may be able to use the pack for a while. When it comes time to replace the cells that are bad,  (the ones you marked), make sure you identify the plus and minus side of each cell before removing them. They are not always marked. Use the photos above to help.When using your volt meter, when the red lead is on the plus and the black lead is on the minus, the volt meter will read normally. If the volt meter shows “negative” volts, the leads are the opposite. If you have a bad cell, use a good cell in the group to find which is plus and which is minus. I will show you were to get the cells below.

    Most cells are hooked together by metal bands that are spot welded on to the cell. Make sure the new cells you buy have bands too. (see the picture above) You will learn where to get new cells below.You use a combination of the ones that are still on the pack and the new ones to make the connection. This is where a little practice makes you better.

   Take the material off that surrounds the cells. (the plastic, cardboard etc.) so that you see each cell. I do not replace this material when I repair mine, but that is up to you. When I am done, I just wrap them with electrical tape or do nothing.

  Once the material is off the cells, they will be loose because they are not bound tightly once you remove the plastic covering. Once you have taken out an old cell and have your new cell in place, use electrical tape to “bind” all the cells back together until you have soldered the bands back on the battery. It is best to replace only one cell at a time to keep from getting confused about what goes where.

    If you have never soldered before, practice on the old cell(s) you take out. It is not hard to learn, you just have to do it a little to get the idea of how hot the things have to be. Make sure the solder flows in a nice smooth puddle. GLOBS are not good and are NOT a good connection.  Sometimes you have to scrape the metal with a sharp object to get it to take solder. You may want to put a little solder on each surface first and then just heat them together to make them bond.

   Remember to replace one cell at a time and make sure you remember which side is which and which side goes to where. In this case the negative goes to the positive of the next battery and the  positive goes to the negative of the next battery as they are in SERIES. (this is NOT the same as when you are using the short removal method above.)

      It is a good idea to mark each old and new cell before you take the old ones out. Remember if you get lost, that all the cells are connected in series which means if you laid them all out, there would be one straight line of cells all hooked from one to the other. Plus from one to the minus of the next one, plus to minus, etc.

    Once you have replaced one or more bad cells, you can bind them all up with tape. I just throw away the plastic that was around them, but it is your choice.

   You may want to replace all the cells at one time. It takes some time, but the pack will then be good for many years to come and even on an 18 volt pack with 14 cells, the cost will only be about $30 total. (much better than $90+ and just as good or better.)

 To find the cells you need, go to Each type of pack has different size cells (physically) and different Milliamp hour rating. (mah). Try to keep them all the same if you can, but do NOT replace a high mah cell with a lower one or you will reduce the usable time of the whole pack. When in doubt, use a higher mah rating.

      Sometimes the ratings will be on the side of the battery, or you can go to the manufacture of the your device site and look up the milliamp hour rating of your pack

    Always remember if you are replacing batteries, to make sure you know which side is + and which side is – before you replace them. If one is shorted, there will be no voltage across it but you can find one that still is good and use that for reference.

Laptop Battery Repair

     Now comes the Laptop battery repair guide. The type of batteries used in laptops are different. You can not BLOW the short out like ni-cad batteries. Please read the information HERE carefully. 

HERE is another source of batteries.

Automotive Battery Repair.

   The batteries used in cars, trucks, golf carts, boats, campers etc. are call lead acid batteries. That's because the plates inside are made of lead and they are surrounded by acid (sulfuric acid). 

WARNING Sulfuric acid can be very nasty stuff if it gets out of the battery and on you or the surrounding areas. If some does get out by mistake, you can neutralize it with baking soda. HOWEVER, always wear safety glasses and plastic gloves when working with any type of auto battery. Also, when a car battery is charging, it puts off a gas that can explode. I HAVE seen this happen and it is not pretty. ALWAYS make sure that any sparks made by connecting and disconnecting wires is AWAY from the battery. At least blow air across the top of the battery if you are going to make a connection near the battery. Even when replacing a battery, I always take a deep breath and blow across the top of the battery which helps to dissipate any gas. 

   As a battery gets older, crap called sulfates begin to form on the plates inside. The more that forms, the weaker the battery gets until it can not be used any more. There is a solution you can put in the battery that will dissolve the sulfates and/or keep them from forming. It can extend the life of a battery by 3 times or more. It works in most batteries I have tried it in, HOWEVER it works the best if you add it before the battery gets bad. 

You can get the solution for $15 including shipping which is enough to do 2 batteries.  You can get it HERE.

   Another way to restore lead acid batteries. You pulse it with high frequency current. This current causes the sulfates to dissolve and return to the solution. The manufacture of this device has been making them for 15 years. They have batteries in their plant that have been there since 15 years ago and still have 90% of their power. (amazing)  Let me know if you are interested in getting one. They are $25 and can be moved from battery to battery.  They work VERY well even on batteries that do not respond to the solution above. 

      Please let me know if you have any questions. Also if anything does not seem clear, I would like to know about it. I try to make this as simple as possible and suggestions are always appreciated.

Also be sure to visit to learn how to save a TON on your gas/diesel costs. Some people are reporting at 200% MPG increase by using a combination of water and gas. That may sound to good to be true, but remember that water has 3 times more available energy than gas. 

 Here is a BONUS you will really like.

Go to
 to learn some great things and save even more money..

 Take Care


  © Copyright 2005-2008 Michael Wood / CSO