Dremel MultiPro Cordless Model 770 Type 1 - Battery Pack Repair




Introduction: Dremel MultiPro Cordless Model 770 Type 1 - Battery Pack Repair

About: Retired healthcare executive with these hobbies: Family, RC Aircraft, Tennis, Biking, DIY and Repair, Travel. Educated as Electrical Engineer, spent 45 years in healthcare IT and C-team leadership.

DO NOT TOSS your Dremel Model 770 Type 1 tool just because the nicad battery pack has failed! You can replace the nicads with new ones! Even 'tho the pack is no longer available from Dremel and battery technology makes you want a tool with lithium batteries do not toss this tool. The light weight and easy-to-handle features of this Dremel tool have not been replaced by newer tool models.

When I queried the Dremel tech support team they advised to not attempt a self-repair.

But, a little help from a related Instructables allowed me to open the battery pack. Replacement of the batteries then became obvious.

Resist the temptation to vary from nicad cells since the Dremel Charger No. 758 that came with the tool is designed for nicads only.

Step 1: Open the Battery Pack, 7.2v No. 757

Detach the pack from the tool. There are 4 small tabs which are part of the black case and hold the red battery pack cover. This pic shows 2 of the tabs. All 4 tabs are shown in a later pic. Using a small thin screwdriver or knife blade, gently insert the blade near the tab while pressing on the red finger grip and applying upward pressure. Work around the pack to release all 4 tabs while pressing upward on the red finger grips on the two sides of the pack. Be gentle! If you break a tab, you're in trouble.

Step 2: The Battery Pack Is Now Open

These pics show the open battery pack with the red pack cover removed. Note the 4 tabs on the black cover. Also note the inside of the red pack cover and where those tabs seat when reassembled.

Step 3: More Pics of the Open Pack

Study the orientation of the two 3-cell packs, red pack cover and AA cells. The two 3-cell packs can only be placed in the black case in one direction - so it will be difficult for you to load the packs wrong. Also note the black rubber O-ring inside the red cover. This serves to hold the batteries against the bottom of the pack when assembled. Do not remove the black O-ring. I took pics of the pack at each step of disassembly to help me later.

Step 4: Remove & Replace Two, 3-AA Cell Packs

Study carefully the polarity of the two three-cell packs before you remove them from the black case. Note that the case bottom is marked with polarity. As the two three-cell packs are withdrawn from the black case, note their orientation. A side view of the packs shows how the cells are assembled. Each 3-cell pack provides 3.6v. The switch on the tool delivers power to the tool from one or both packs, thus the 2-speed tool.

When looking at the pack bottom note the silver "buttons" which are the contacts for the tool. These "buttons" may need to be added to the AA batteries by you or your cell supplier. The battery size and pack construction are critical and must be EXACT replacements for the bad ones.

My local Batteries Plus Bulbs store had the AA cells, tools and connector plates to make the replacement packs for me. I left one pack with them to serve as a model. Their price for the packs was very reasonable. Turnaround was one day.

I am now a happier DIYer with one of my most favorite tools performing as good as new!



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    11 Discussions

    Thanks for the advice. I have a Dremel 770 (with blue, not red plastic) that's got to be 20 years old and still running on the original ni-cads, which still hold a good charge. If they ever do fail, it's good to know they can be easily replaced. I have an even older corded Dremel for heavier jobs. Both seem better-built than the new ones.


    4 months ago

    We have the Model 770 and cannot get the battery pack to slide open....how to do this?

    I actually have this exact dremel and the batteries last me about 5 minutes. Thanks for the instructable!

    Great Instructable. I have been rebuilding battery packs for scientific instruments for about 25 years and in spite of what you have been told, you can replace NiCad AA cells with rechargeable NiMH cells available in any hardware store, camera store or drug store. The advantage of NiMH cells (which have the same voltage as the NiCads - 1.2 volts) is that they are more readily available and have higher power density than the NiCads. The disadvantage is that you will get fewer charge/discharge cycles our of them before the battery has to be rebuilt again - about 300 cycles for an NiMH vs. 500 for a NiCad cell. I use the same charger as for the NiCads. i.e. the charger that came with the equipment. Because of the higher power density you will get about twice the run time on a charge as you would with NiCads. I fasten the cells together using the metal strips pulled off of the defective NiCad packs, but if there is room, you can also use hookup wire for this.

    NiMH AA cells come in different power ratings, up to 2800 mAH (Milliamp-Hours). Get the highest rated cells you can find, for maximum run time.

    1 reply

    yes they operate at the same voltage. they have slightly different charging requirements though and if you want to use the same charger and not have to replace your nimhs in half the time you are as the author pointed out better off sticking with nicd. and yes i have saved several power tools myself as well.


    2 years ago

    ok. I have to confess...it's Sunday morning, and I was too lazy...at first...to put on real clothes and shoes and run out to the shop. But curiosity got me, and I have time...Church isn't for another hour yet. Anyway, I went and found mine and the battery has a small + and - marked on it. I pulled it apart and put in 4 alkaline AA batts. Held the pack in place, and connected the battery pairs with strips of kitchen foil. Viola. it works...and with good torque. almost full power. Time to 3d print a battery holder.? Thanks for the push in the right direction.

    1 reply

    Thx for your comments. I have edited the description to add comments regarding the two 3-cell packs. The black case determines how the packs are loaded - design of the case and the polarity shown on the bottom of the black case dictate the orientation.


    2 years ago

    forgot to ask...can you post a simple diagram of the orientation of the batteries in relation to the battery pack alignment? Thanks.


    2 years ago

    Thanks!!! I have this tool and the battery charge is not lasting very long any more. I have not been able to find a new pack for a price that makes sense, but I'm not ready to scrap the tool. This will work well for me. I'm also wondering if it might run off of a temporary non-recharge pack (alkaline and black tape). I did an 18 volt drill battery this way way once...2 rows of 3 - 9v batts in parallel...then connected in series to juice the drill. Worked for small stuff, but of course they got a bit hot when you needed a lot of torque for any extended time.