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Rebuilding a Dewalt 6ah Battery Pack

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  • Rebuilding a Dewalt 6ah Battery Pack

    I bought a dead 6.0 ah Dewalt battery on Ebay for for $40. 4 of the 10 batteries were toast. Internally shorted. They are 20700 size and by Sanyo. The model number, 7423, doesn't produce any specs on Google

    I have some 18650 batteries from laptop packs, that are 2400 mah to 2600 mah. LG and Samsung, From looking around, these are high quality.

    Can I mix the Sanyo 20700 and the LG 18650? If so, the repair is FREE!

    Keep in mind, even if the ah drops to 5.0, the price of a 5 ah battery is $140. A 6.0 is $177.

    If the cells don't mix, I can still buy 20700 for $8 apiece.

  • #2

    I belise that the manufacturers recomment that you not mix brands and types.
    In this case I believe that the 18650 and the 20700 batteries do not have the same maximum current capacity. The suggestion is that series connection of different types could prove to be dangerous.


    • #3
      Don't mix battery size, type, brand etc. All must be identical for charging or the likelihood of failure is great. Buy a set from one of the various on line sources.


      • #4
        I buy all my batts from nitecore now. Here is a 2600mah 18650. JR
        My old yahoo group. Bridgeport Mill Group


        • #5
          It would appear that one may buy a new complete battery pack for $110.00. Why would you by a used one of questionable utility?

          Just curious by the way.

          Last edited by Bented; 01-22-2021, 10:15 PM.


          • #6
            Originally posted by Bented View Post
            It would appear that one may buy a new complete battery pack for $110.00.
            (grin) On such great deals, beware the shipping!


            • #7
              Going to go with the $7 Sanyo 20700. Can't find the exact model number, but the numbers are all close. $40 + $28 = $68. Again, shipping. Still cheepa than new.


              • #8
                never mind
                Last edited by J Tiers; 01-23-2021, 12:18 AM.
                2801 3147 6749 8779 4900 4900 4900

                Keep eye on ball.
                Hashim Khan

                It's just a box of rain, I don't know who put it there.


                • #9
                  Cheap lithium ions have a max current of 1 to 3 C. Compared to different ones which can handle 10C.

                  I have some ultra fire 18650 with a short circuit current of 7 to 9 amps
                  and i have some from toshiba laptops with a short circuit current of 20 amps.

                  Someone gave me a 5 cell bosch pack with 20mm cells in it and my guess is the short corcuit current is 200 amps.


                  • #10
                    do not mix capacities or chemistries. you'll be short cycling and/or overcharging the highest or lowest one every single time, and that is a sure-fire recipe for cell failure (read: fire)

                    just go buy new ones if you have to ask these kind of questions. burning your shop down is not worth it.

                    I have recelled power tools before. If you have to ask the difference between a power cell and an energy cell, go read up on it first.


                    • #11
                      John Buffum how do you plan to terminate the cells?


                      • #12
                        Whether this would work or not will depend on lots of factors. The good brands have balancing circuits that will keep the individual cells at the same voltage pretty well when charging, but during high discharge rates the cells will almost certainly be discharged unevenly. That will considerably shorten the life of the pack and could conceivably cause a catastrophic failure of an individual cell during high discharge use.

                        Each individual cell has its own capacity and also what is called internal resistance. The internal resistance determines how evenly the load between cells is shared. If the cells don't all have the same internal resistance, they will not charge and discharge evenly. To repair a lithium chemistry pack it is probably a good idea to replace all the cells at once with a matched set rather than try to add a few individual cells.


                        • #13
                          To make a Battery you need cells.

                          Those cells should be from the same manufacturing lot number, JR
                          My old yahoo group. Bridgeport Mill Group



                          • #14
                            Originally posted by JRouche View Post
                            To make a Battery you need cells.

                            Those cells should be from the same manufacturing lot number, JR
                            AHA! So that's what the last 4 digits are! No wonder there isn't specific info.

                            The replacement cells are inbound. Going to go with the Sanyos. They match on size and rated capacity. Not going to replace all. But, for awhile, I'll store the battery pack in a stainless steel bucket with a 3/8 steel lid.

                            Machining has always been risky. Look at what happened to the builder of the first commercial steam locomotive. It ran over him.


                            • #15
                              There are risks and then there are unnecessary risks....