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[Solved] Makita 7000 Screwdriver Battery Regeneration: Ni-Cd to Li-ion Conversion & Overcharge Protection

norwidus66 6258 16
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What is the third contact on an old Makita Ni-Cd battery pack, and how should it be connected when converting the pack to Li-ion with protection circuitry?

The third contact is the battery temperature sensor output, i.e. a thermistor, not an extra minus or protection lead [#16965886] [#16965890] It should be connected the same way as in the original pack, between ground and the third contact [#16971334] [#16971470] If you convert the pack to Li-ion, the thread also notes that you should use a proper balancer/BMS and high-current cells such as INR18650, and that the original charger may not be suitable without a balancer [#16971366] [#16971376]
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  • #1 16965823
    norwidus66
    Level 7  
    Posts: 14
    Rate: 4
    Hello all.
    Recently, I have regenerated some screwdriver batteries. Everything was fine until my brother needed a battery for the old Makita - a 7000 type whip. After dismantling, a problem appeared. Well, this battery (ni-cd) has a third "pole", with which I have not met so far. It looks like an additional minus, a bit specific, on the side of the uninsulated housing of the last cell. I believe that the last cell contains an overcharging and short-circuit protection system - which results from the technical data of the battery. My problem is whether by installing a new set of two li-ion batteries (3.2v) and using PCM to derive a minus on the "third" Makita 7000 Screwdriver Battery Regeneration: Ni-Cd to Li-ion Conversion & Overcharge Protection pole"????
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  • #2 16965886
    bubu1769
    Level 43  
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    This third pole is the output from the temperature sensor (that rectangular tablet attached to the cell) without it, some chargers won't even start charging the battery.
  • #3 16965890
    Freddy
    Level 43  
    Posts: 19997
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    This is a common thermistor to control the packet temperature.
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  • #4 16967896
    norwidus66
    Level 7  
    Posts: 14
    Rate: 4
    Thanks. Everything is difficult until it gets simple :D
  • #5 16971320
    norwidus66
    Level 7  
    Posts: 14
    Rate: 4
    Well, there was a trifle - that is, the thermistor is moved but how do I understand it to connect to the third pole outside the PCM circuit?
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  • #6 16971334
    Freddy
    Level 43  
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    Connect as it was - from what I remember, it should be between the ground and this additional contact.
  • #7 16971352
    norwidus66
    Level 7  
    Posts: 14
    Rate: 4
    I could not quite like it was because I replace Ni-cd li-ion and I have to install protection against discharge and overcharge mentioned "BMS Protection PCB Board PCM"
  • #8 16971366
    bubu1769
    Level 43  
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    Will you be using the original charger or regular power supply?
  • #9 16971367
    norwidus66
    Level 7  
    Posts: 14
    Rate: 4
    Original
  • #10 16971376
    Freddy
    Level 43  
    Posts: 19997
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    It's just that you have to give a new charger with a balancer and the cells have to be high-current, eg INR18650.
    Why don't you regenerate the package, there are companies that do it and it does not cost expensive, starting from PLN 70.
    Enter "makita 7000 battery" on Allegro
  • #11 16971386
    norwidus66
    Level 7  
    Posts: 14
    Rate: 4
    I will just install the balancer in the battery system. 70 dych for regeneration on ni-cd with dubious 1500mah. I have a high-current (20A) samsungi for PLN 50. New 2500mah lithium-ion art. They will walk for a few years, not two or three, and it's not good ...
  • #12 16971394
    Freddy
    Level 43  
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    norwidus66 wrote:
    I have a high-current (20A) samsungi for PLN 50
    INR type?
    You get the normal warranty on regeneration. Anyway, how you want - your choice, your screwdriver.
    If you do not give INR18650-25M cells (this M is also important), you will get a little bit and it will fall.
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  • #13 16971402
    norwidus66
    Level 7  
    Posts: 14
    Rate: 4
    That's exactly what I have. So how with this thermistor - directly from ground outside the balancer - right?

    Moderated By Mirek Z.:

    I have removed the link to the auction forbidden by the regulations. https://www.elektroda.pl/rtvforum/faq.php - p. 3.1.18.

  • #14 16971470
    bubu1769
    Level 43  
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    Yes, thermistor under ground and third contact.
  • #15 16971484
    norwidus66
    Level 7  
    Posts: 14
    Rate: 4
    Thanks!!! Now it's downhill - some fun with soldering, balancing the tabs and it will be OKI
  • #16 16971522
    Freddy
    Level 43  
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    norwidus66 wrote:
    Thanks!!! Now it's downhill - some soldering fun
    How many were originally 6, as I can see. So you give 2 lithium?
  • #17 16971712
    norwidus66
    Level 7  
    Posts: 14
    Rate: 4
    It was 6 x 1.2v and I would give 2 X 3.7

    Added after 3 [minutes]:

    auction number on Allegro 6990907686
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Topic summary

✨ The discussion revolves around the regeneration of a Makita 7000 screwdriver battery, specifically addressing the conversion from Ni-Cd to Li-ion technology and the integration of overcharge protection. The user encountered a unique third pole in the Ni-Cd battery, identified as a thermistor for temperature monitoring, which is crucial for the charging process. Participants provided guidance on connecting the thermistor to the new Li-ion battery setup, emphasizing the need for a Battery Management System (BMS) to prevent overcharging and discharging. Recommendations included using high-current INR18650 cells and ensuring compatibility with the original charger. The user expressed intent to install a balancer in the battery system for improved performance.
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FAQ

TL;DR: Makita 7000 packs use 6×1.2 V Ni‑Cd; typical Li‑ion conversions use 2×3.7 V in series. “This third pole is the output from the temperature sensor.” [Elektroda, bubu1769, post #16965886] Why it matters: This FAQ helps DIYers safely convert Makita 7000 Ni‑Cd batteries to Li‑ion while keeping charger compatibility and over‑temperature protection.

Quick Facts

What is the “third pole” on the Makita 7000 battery?

It is the thermistor lead used by the charger to monitor pack temperature. Without this sensor connection, certain chargers refuse to start charging as a safety measure. Treat it as a temperature-sense terminal, not a power pin. [Elektroda, bubu1769, post #16965886]

How do I connect the thermistor when converting to Li‑ion with a BMS/PCM?

Keep the thermistor in-circuit and wire it between battery ground and the third contact, outside the cell-balancing path. This preserves temperature monitoring while the BMS manages voltage/current protection. As one expert put it: “Connect as it was—between ground and the additional contact.” [Elektroda, Freddy, post #16971334]

Can I keep using the original Makita Ni‑Cd charger after the Li‑ion conversion?

Use a Li‑ion charger with cell balancing. The original Ni‑Cd charger is not suitable for charging Li‑ion chemistry safely. A modern charger with a balancer ensures proper cutoff and equalization for the 2‑series pack. [Elektroda, Freddy, post #16971376]

Which cell configuration replaces the stock Makita 7000 pack?

The original pack is 6 cells × 1.2 V Ni‑Cd. A common Li‑ion retrofit uses 2 cells × 3.7 V in series (2S). This yields the required nominal voltage while reducing cell count and weight. Verify tool current demands before finalizing. [Elektroda, norwidus66, post #16971712]

What Li‑ion cells are recommended for a drill/driver conversion?

Choose high‑drain INR18650 cells; INR18650‑25M is specifically recommended. Low‑drain cells sag under load and shorten runtime. Matching high‑current capability helps the tool maintain torque and reduces stress on the BMS. [Elektroda, Freddy, post #16971394]

Is there a minimum current rating I should target for the cells?

Use cells capable of around 20 A discharge for robust performance in power tools. A user referenced 20 A Samsung cells as a good fit for this application, aligning with high‑drain requirements. [Elektroda, norwidus66, post #16971386]

What is a BMS/PCM, and do I need one?

A BMS/PCM protects Li‑ion packs from overcharge, over‑discharge, and short circuits, and may balance cells. Include it in the converted pack to prevent damage and safety risks. Route the thermistor separately to the third terminal. [Elektroda, norwidus66, post #16971352]

Will the charger work if I omit the thermistor connection?

No. Some chargers will not initiate charging without the thermistor signal. This is a safety interlock to avoid charging a pack without temperature feedback. Always restore the third terminal wiring. [Elektroda, bubu1769, post #16965886]

How do I physically wire a 2S Li‑ion pack for the Makita 7000?

Basic steps: 1) Build a 2S stack with appropriate nickel tabs. 2) Connect the BMS: B−/B1/B+ to cells, P−/P+ to tool. 3) Wire the thermistor between ground and the third contact. Confirm continuity and insulation before closing the case. [Elektroda, bubu1769, post #16971470]

Can I balance the cells inside the battery housing?

Yes. Install a balancer or a BMS with balancing inside the pack. This supports even cell voltages during charge and discharge, improving longevity and safety for your 2S setup. [Elektroda, norwidus66, post #16971386]

What is a thermistor and why is it in the pack?

A thermistor is a temperature‑dependent resistor used for thermal monitoring. The charger reads its value to detect over‑temperature and control charging. Keeping it connected ensures safe operation and prevents charge refusal. [Elektroda, Freddy, post #16965890]

What’s the failure mode if I pick the wrong cells?

Low‑drain cells cause voltage sag under load, weak torque, and early cutoffs. As noted, without the right INR18650‑25M‑class cells, performance drops quickly and pack life suffers. [Elektroda, Freddy, post #16971394]

Do I need to modify the tool terminals?

No terminal changes are required if you preserve the three contacts: positive, negative, and the thermistor lead. Ensure the BMS output goes to the main +/- while the thermistor remains on its own line. [Elektroda, bubu1769, post #16971470]

Any soldering tips for assembling the pack?

Use spot‑welded nickel strips when possible. If soldering, work quickly on tabs, not cell cans, to avoid heat damage. Verify insulation and strain relief before reassembly and test with the charger. [Elektroda, norwidus66, post #16971484]

Will I notice better runtime after converting to Li‑ion?

Yes, when using high‑drain 2500 mAh Li‑ion cells and proper balancing, users report multi‑year service and stronger performance compared to tired Ni‑Cd. Keep thermistor and use a Li‑ion charger for best results. [Elektroda, norwidus66, post #16971386]

What’s the quickest way to confirm my wiring before first charge?

Check that the charger starts only with the thermistor connected, and that pack voltage matches a 2S Li‑ion (about 7.4 V nominal). If it refuses to start, re‑verify the third terminal wiring. [Elektroda, bubu1769, post #16965886]
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