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Recycling old batteries

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  • Recycling old batteries

    I have several DeWalt NiCad 18 volt battery packs for cordless tools. All are defective: low power output, won't hold a charge and show as defective when I attempt to charge them. Not complaining: I got close to 10 years use. I have gone the new tech route & converted to Li-ion so these aren't needed for my tools.
    Is it possible that the whole pack tests as bad because a few cells in each pack are degraded? Wondering if opening each pack & testing the individual cells has any merit. Can I check each cell in-circuit or must I remove & test each individual cell? How would I know a cell is good or bad? Assuming I get enough good cells I would rebuild to have fewer good batteries.
    I know that this is time-consuming and probably not worth the effort but I want to satisfy my curiosity.

  • #2
    At that age. not really worth the effort. You really need a balanced chain of batteries for good results and 10 year old nicads are pretty much shot. Many may be internally shorted. Adding a few new cells can make the remaining weak cells decline and die even faster.

    You can test each when connected together by charging that one cell and discharging it at a set rate until the terminal voltage is reached. Obviously you need a suitable power supply.


    • #3
      NICD packs definitely can have one or two bad cells. Yes, you often CAN replace them and do well.

      This is because the packs have zero cell protection, in turn because the cells do nothing dramatic when abused, unlike lithium.

      WHEN you try to "get just a couple more holes drilled", one of the cells is the lowest capacity. It runs out of charge first, voltage drops to zero, and then it "reverses", it begins to charge backwards due to the current still flowing from other cells. Two problems........ First, this quickly destroys the cell. Second, it really DOES charge backwards, so it not only does not provide its voltage, it also subtracts a SECOND amount of voltage equal to its charging voltage. Battery voltage drops fast, as you who do that will notice.

      So, you have at least one bad cell, that acts like it charges up, but drains to zero when not used, and you have a "weak pack".

      If you catch it before more cells are reversed and destroyed, you can replace the one or two bad ones and have a working, if less than perfect, pack. If you have two or three packs, you can uften get one or two usable ones from them.


      Problem is, NICD are getting scarce, some sizes are not available, and if you cannot get a lithium upgrade for your unit, you will be throwing away the tool just because of batteries.... so it can be worth it to repair the packs.

      Keep eye on ball.
      Hashim Khan


      • #4
        I had an old 12V cordless drill that the batteries gave up the ghost on. I replaced them with a cable with jumper clips and used it on the boat. You could probably do something useful with 18V tools also. Don't know how well or poorly they'd behave on a 12 V car or boat battery.
        "A machinist's (WHAP!) best friend (WHAP! WHAP!) is his hammer. (WHAP!)" - Fred Tanner, foreman, Lunenburg Foundry and Engineering machine shop, circa 1979


        • #5
          I found an interesting website dedicated to reworking NiCad and NiMH battery packs and cells:

          Here is a source for replacement battery packs:

          I recently took apart my rarely used B&D hand vacuum, which had 15 Sub-C NiCad cells, most of which were dead. I might order a replacement set for about $20:

          But I can get a complete new vacuum for about $28, although not very good review:

          Or one with lithium batteries for $30, and better reviews:

          Or an open box lithium B&D for $15:

          (Funny thing, when I tried to post with four images, it said I had six. I found that the extended URL for two items had characters that were translated to emoticons and counted as images
          Last edited by PStechPaul; 10-21-2018, 04:26 PM.

          Paul , P S Technology, Inc. and MrTibbs
          USA Maryland 21030


          • #6
            Rather than rebuilding my DeWalt battery packs, I just ordered some generic replacements off Amazon. They were about $16 each delivered and have been working great for well over a year. Had I previously realized how cheap the replacements were and how well they worked, I would have never gone any other route.
            Location: North Central Texas


            • #7
              I have the Porter Cable Drill-Flashlight set from nearly 20 year ago. The cells are sub C tabbed. I rebuilt them as needed with
              import tabbed cells 4 times until the NMHi cells became available. WOW!! What a difference. No more self discharge. Always ready
              to go and more power longer. I replaced the original charger with a compact switched mode NiCad/Nmhi capable type.
              The batteries are always the primary failure of otherwise excellent power tools.
              RichD, Canton, GA


              • #8
                They can definitely be rebuilt. I did an article in the Dec 15-Jan 16 Machinist's Workshop magazine on how I rebuild mine, "The Cheap NiCad Rebuild".

                I have seen NiCad battery packs being rebuilt on a professional basis for many decades. This goes back to the days when a 12V NiCad battery pack for professional use cost between $100 and $400 so the incentive to rebuild them was very strong. IMHO, it is not a good idea to just replace individual cells. If one or two cells have gone bad, then the rest are on their last legs as well. Costs have changed so, if you are going to take the trouble to rebuild them, then just replace all the cells. See below for more on the cost factor of that.

                Some of the points that I made in that article were:

                1. An inexpensive source of new cells is the NiCad packs that are available at Harbor Freight. The cells are made as a generic item and I think that there is little or no difference between the cells used in a $50 battery and those used in the HF packs that can be had for less then $10. I did say "cheap" in my title and it is justified. I got several HF batteries on sale for around $7 each and they had enough cells for a full 18V battery.

                I have batteries that I have rebuilt with cells from HF batteries that have lasted for three or more years. In fact, the cells in the HF batteries were full sized while the original B&D batteries that I rebuilt had sub-sized cells that gave significantly less time per charge. I simply removed the spacer that B&D had in their battery packs to take up the extra space and the full sized cells fit perfectly.

                2. You should not solder directly to the cells because the heat will damage them. The professional battery rebuilders use a welding device that welds the straps to the cells without passing any current through the cell itself. It uses two closely spaced electrodes to create two spot welds at once so the heat is localized to the area of the welds and the process if fast so there is not much of it. Most home shops do int have one of these welders, but if you purchase the already assembled cells, the straps are already welded to the cells. Some connections can remain as-is. And where you need to rearrange them, you just cut the straps half way between the cells and that gives you two tabs on each cell that you can easily solder to without damaging the cell.

                3. The space inside the battery's case is probably too small to allow actual wire to be used. I describe how I used 12 gauge copper wire and some tin-knocker skills to convert this wire into a strap. Not hard and you can form it into curves as you go.

                Those are some of the points that I remember. There was a complete description of the rebuild process in the article.

                PS: I suspect that the sub-sized cells were a sales strategy by B&D: they made the battery case to hold full sized cells but installed the smaller ones because they were cheaper. Then they built their extended life batteries with the full sized cells in the same case and charged a significant amount more for them. What a deal - for them anyway. I have to wonder how many other manufacturers used the same strategy.
                Paul A.
                SE Texas

                Make it fit.
                You can't win and there is a penalty for trying!


                • #9
                  Originally posted by Paul Alciatore View Post
                  ...... I have to wonder how many other manufacturers used the same strategy.
                  All of them, probably. Standard deal. And not a cheat, the larger cells cost more. This way they only needed one size plastic molded part, and nobody complained about a "too big, too fat" pack, because they were the same size.

                  Keep eye on ball.
                  Hashim Khan