Picture of 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.
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Step 1: Opening the pack

Picture of 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

Picture of 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

Picture of 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.
russ_hensel1 month ago

Just a note to let you know I have added this to the collection: Cordless-Drill-Battery-Maintenance !


Take a look at a bunch of different/similar approaches to this project.

bphipps11 year ago


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!
ising2 years ago
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?

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:
hansonsux5 years ago
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. 
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.
stuuf (author)  carpespasm4 years ago
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.
LinuxH4x0r6 years ago
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.
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?
you could TRY conductive glue.

Definately be careful though. Soldered wires can handle a fair bit of current.
I don't actually know how much power the glue can handle.
low powered stuff should be fine, but power tools can draw a lot of juice.
Soldering isn't really much of a mystery--I haven't looked, but I bet there is an instructable somewhere around here on how to do it.  The tools aren't all that expensive, either.  Have you ever tried it?  (I'm trying to be encouraging--hope it doesn't come across as snotty.)
Just to note: soldering to non-tabbed cells isn't a great idea. You have to really get the whole end of the battery way hotter than it's made to get before solder will stick directly to the battery. under the positive end there's a small spring controlled pressure valved that keeps the cell from exploding if it's overcharged or leaking it's guts.

If you're dealing with something that's hard to get a battery for and just want to see if you can get it going that's not the worst thing in the world and NiCd and NiMH batteries can take enough abuse that soldering right to them won't outright kill them, but it's not really good for them either. Most battery stores and cordless tool repair and service shops will weld tabs on your cells or rebuild packs like this pretty reasonably too. Soldering to tabbed cells is A-OK too.
i work in the insulation industry and there is a foil tape used for duct wrap foilbacked insulation mainly . try . although im not sure how conductive it is i do know it has a very thin layer of adhesive.... hope that helps
Its wont work well unless you are using the non sticky side of the foil tape plus you have to steal wool the non sticky side to make it conductive it has a laminate on it or a sealant of some kind
no, but you can use rare earth magnets
hansonsux5 years ago
Just keep in mind that NiMh are more sensitive to overcharge damage, so take extra care to not leave the batteries on the charger for no longer than needed.  This overcharge damage happens to NiCad as well, but just more slowly. 
wow...did not know at all that there were standard batteries inside this thing...i'm totally gonna hack mine when it loses the charge.
stuuf (author)  PlayPatterns5 years ago
power tools, cordless phones, laptops... the battery packs are always made of standard cells. Even less common cells like SubC or 18650 are cheaper than paying for a whole new pack.
shyamhegde6 years ago
Thanks for the instructable! Useful one for me.
The charger is meant for NiCad cells, not for NiMH. It will charge them, and it will take longer as you stated, but they may be damaged in the process.
Just a quick warning: There is a lithium-ion version of the cordless Dremel tool. Don't try this hack on that one!
NerdMaster6 years ago
I have one of these, and you are dead-on about the battery life. I had no idea there were standard batteries inside. Thanks for the Instructable.
Sandisk1duo6 years ago
Nice instructable!