Cordless Dremel Battery Pack Upgrade





Introduction: Cordless Dremel Battery Pack Upgrade

The cordless Dremel Multipro rotary tool uses a rechargeable battery so you work anywhere without having an AC power source. Unfortunately, like most power tools, the battery pack is filled with cheap nickel cadmium cells that don't last very long on a charge and will start to wear out after a couple years. Since the pack uses standard AA size cells, you can replace them with high-capacity nickel metal hydride cells for a battery that lasts 3 times longer.

Step 1: Opening the Pack

The battery pack is held closed by four small plastic tabs on the back. Push them out of the way with a small screwdriver and the blue part will come off.

Now remove the two groups of NiCD cells. They are 700mAh AA's, with little tabs holding them together. Each group is 3.6V, so the tool connect them in either series or parallel to select high or low speed.

Step 2: NiMH Cells

You'll need a total of 6 nickel metal hydride AA cells, with solder tabs attached. You can buy these from a number of online stores for a little under $2 each. Just make sure you get the ones with tabs so you can solder them together.

Total price for all 6 cells from various stores: 2300mAh, $10.80 2200mAh, $9.96 2300mAh, $10.92

Step 3: Solder Into Packs

Separate your new batteries into two groups. Arrange them the same way as the old pack, in series. To make sure you have the polarity right, you can check the groove on the end of each NiCD cell that indicates the positive end, look at the +/- markings on the outside of the pack enclosure, or check the old pack with a voltmeter.

If your cells have short tabs like mine, you'll need to splice them together with a small piece of wire.

Once you have them connected in the right order, solder the tabs together and check the total voltage to make sure everything conducts.

After they're soldered, wrap some tape around each pack to hold them together and cut off the bottom tabs.

Step 4: Assemble and Test the Pack

Place the new cells into the plastic pack enclosure. Before you close everything up, plug the pack into the Dremel and test it on both speeds. It won't stay in very well by itself, so you'll have to hold it in to keep electrical contact.

Once you're sure everything works, snap the blue plastic part back in to close the battery pack. You should be able to charge it with the original charger, although it will take much longer because of the higher capacity cells.



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    34 Discussions

    Thanks; with my mediocre soldering skills I would not have tried this, but it's working now. On high speed, the speed is really high... will the motor keep up? I might just use low speed (which is higher then the old high speed) until I know...

    I was searching for a lithium ion battery pack upgrade for my dremel and came across this upgrade. I had to do something, the old ni-cad battery would only last me 5 min of run time.

    I had to remove the o-ring in the battery case and put a little plumbers putty in its place. After that everything fit perfectly.

    It runs great but I'm still waiting for the thing to finish charging. It's still blinking after 6 hours.

    this must be super old, i don't think any cordless dremels sold nowadays use that kind of battery, that thing is huge and it looks like it's from the stone age! lol... I have a dremel 8220 with a lithium ion battery that is much smaller. the battery model number is B812-02... anyone know if the this battery can be hacked as well?

    1 reply

    Yeah, most power tools have finally converted to lithium ion now. The only ones I've taken apart are Ryobi packs which use 5 18650 cells to get 19.5V nominal (or 10 in the high capacity packs). I assume Dremel uses 3 cells in theirs, but I'm not sure what size they are. Generally li-ion has a longer cycle life so they don't wear out as quickly as the old NiCd stuff but you should be able to use basically the same procedure to replace the cells.


    If I use battery's suggested will my standard dremmel batt charger still charge new pack or will I need another charger?

    Many thanks


    I sure am glad I found this. I was about to go to Home Depot and spend Money!

    My dremel battery pack is #755 There are only 4 batteries, 4.8V 0.7Ah. The batteries are not soldered, they are taped. Can I still replace with NiCd or NiMH?

    I have the 855-02 pack, which has shorter blue disengage pieces on either side than the one pictured.

    The 855-02 does not come apart by pressing-in the four little tabs at the seam between the blue and black sections - the two blue disengage pieces appear to be catching on the black section of the body as the blue base tries to separate.

    Has anyone disassembled an 855-02 pack?

    Got a hint, please?


    1 reply

    I had the same issue with the 855-02 pack. Just insert a thin screwdriver at the point between the blue and black plastic directly above the thumb piece and push. You will notice the thumb piece moves in and pull up while you do this. Push in the two tabs to the right and left of it with a combo of pushing and twisting the screwdriver and then repeat on the opposite side. Now I just need to figure out where to get these replacement cells on the cheap. Any ideas?

    These are the cells in the 855-02:

    Also NiMh can suffer plate oxidation from long periods of being below 1v (dicharged).  Say if you had a NiMh upgraded power tool that fell into disuse for a couple of years.  When you go to use the tool again, the battery may have lost capacity.  NiCad most universally jumps back to life.  The plate oxidation depends on brand since some brands are more resistant to oxidation than others.  Just something to think about. 

    7 replies

    Having worked for a couple years at a battery store where we rebuild packs like this frequently most people who let any rechargeable battery regardless of chemistry sit for longer than a year wind up with either a severely weakened pack or one that's just totally dead. Most people don't realize that more or less all rechargable batteries self-discharge when they're left unused, so even if it was fully charged when you put it away at 1-2% self-discharge per day most batteries will be run down a half year later, and when it's sitting around dead for months later it's not likely to come back too well when you do try to charge it again.

    TL:DR - top-up rechargable batteries up every 2-3 months even when you're not using them.

    Sanyo Eneloop rechargeables come precharged, and hold 80% of the charge for three years. I just got new ones, and my old ones still hold up fine. They last for the longest time in r/c cars... :)

    Sounds like the same thing as Rayovak's hybrid rechargables. Good stuff if you can find them.

    It also helps if you use a decent charger that can run at higher current with a proper cutoff circuit and do a discharge cycle every once in a while instead of the $3 transformer+resistor that comes with every nickel-based cordless power tool. Unfortunately you almost always have to take apart the tool or the charger dock to get direct access to the battery pack to stick the charger on. And finally rebuild the pack once it gets really dead.

    With a little ingenuity you can upgrade your original charger pack as well, so that the battery will still fit w/o the hassle ;-)

    Truth. We use a Cadex to test rebuilds where I work and it can also refresh and cycle packs. I've had a couple of my personal drill batteries that I thought were totally shot and started out dead shorted which came back up to 94ish% capacity. That said the packs were otherwise well taken care of and still should have otherwise been expected to be in their usable life.

    A lot of people hear about this sort of thing and assume it's a sure-thing or a magic for their old battery packs. This is unfortunately not so. If they're really old and/or leaking or something there's a chance, and generally nicads hold up to more abuse than any other major chemistry.

    You can also leave the charger(s) plugged into a power strip with a timer on it. I find one hour a day keeps drill/dremel/flashlight/etc. charged and ready for use all the time, without running the charger at them all the time.

    Very nice! If you are lucky enough to have a tig welder you can use that to tack strips of metal to regular batteries instead.

    1 reply

    Ive pretty much given up on my cordless cuz the low batter power. I dont solder or weld. Might there be some kind of metalic tape?