Makita Ni-Cd Battery Pack (1250)

I took apart an old Makita cordless drill (M651D) to take a look inside. It was very well designed and friendly to servicing, meaning it was easy to take it apart and put it back together still in working condition. The drill is still good, it’s too bad its NiCad battery packs are worn. Which made me think: what if I can hook up another battery to this drill? Since I wanted to leave the drill itself intact, I will remove NiCad cells from the battery pack and solder new wire in its place.

This is easier said than done. While Makita’s DC1414 charger and M651D drill were designed for easy disassembly and servicing, the Makita 1250 battery pack is sealed up tight. There were several YouTube videos of people taking these battery packs apart, and I can see it is glued together all around the perimeter between black and orange plastic pieces. The only way inside is to chisel apart durable ABS plastic.

Fortunately, it appears the battery cells themselves were not glued in place. So I’m going to try a different route and cut from the bottom with my Cutra Wondercutter S. This is not the safest of activities but I’m willing to cut near battery cells because of the following:

  • They have no remaining charge to arc or cause problems.
  • These NiCad cells have a sturdy steel can exterior.
  • Even if I manage to puncture a can, NiCad chemistry is less volatile than lithium-based chemistries.

I would be very hesitant to cut near lithium-based batteries if they were 18650 (or similar) steel cylindrical cells. I would not try this at all if they were soft-skinned pouch cells.

I started with a small cut to find the depth of cut. This also gives me location of a single NiCad cell and lets me get a rough guess of where the rest of them are.

I gradually cut more and more of the bottom away. The Wondercutter does a pretty good job with ABS, cutting partially with its ultrasonic action and partially with the heat generated by said action. There’s definitely the smell of melted ABS but much more pleasant than if all the cutting were done by melting ABS with a heat knife. It does scratch the surface of cells, but didn’t come close to puncturing them.

I had hoped the NiCad cells would just drop out the bottom, but they were actually held very tightly by the base. Around the perimeter are small triangular pieces of plastic that follow the curve of each cell and wedge the entire pack in place. I had to cut all around bottom perimeter in order to remove those wedges. The final two were just inside the plastic clips that I wanted to keep so it could still be installed on the drill.

Annoyingly, those two final wedges were still strong enough to hold all batteries in place! I had to carefully cut away one wedge before I could dislodge the entire pack of cells.

These cells will go to a proper channel for NiCad battery recycle. But before that happens, I want their power contacts.

Those contacts were attached with a battery spot-welder and could be freed with some… mechanical persuasion.

Earlier I took apart a car battery charger, so I had a pair of wires handy and already designed for high amperage around 12V. I soldered them to salvaged battery contacts and reinstalled them inside battery enclosure. Reinstalled back onto the drill, it becomes a corded drill powered by wires. I don’t know what alternate power source I want to connect to these wires yet, but this hack of a Makita 1250 battery enclosure lets me supply power to an unmodified M651D drill.

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