Repairing a Boda cordless drill: new Li-ion cells, spot-welded pack assembly. A friend was about to throw out a dead drill — both batteries dead, the drill dead too, only the charger worked. I fixed it, so I’m not giving it back, I’ll use it myself

A dead Boda cordless drill from a friend: motor shorted and smoking, both packs dead; swap in the motor from an old drill, fit 3 × 2500mAh 12C power cells (12mΩ internal resistance), spot-weld in place over the original lead positions with a compact welder, and revive both packs

A friend gave away a cordless drill set (charger + drill + two packs), all dead: on a DC supply the back smoked as soon as it was powered, and inside the motor was shorted; the packs had been killed by the heavy current too. The creator happened to have an unwanted Boda drill (already taken apart, poor to use, slow with no high-speed gear), so its motor came out to replace the bad one, then the cells. Cells chosen: 2500mAh 12C power cells with only 12mΩ internal resistance, three of them. The original pack is fairly complex, wires everywhere plus a thermal cutoff, so the creator’s approach is not to strip it fully when welding — you’d lose track of which wire is which — but to weld straight over the original positions. This nickel strip welds fine with this compact, light welder, and once welded it won’t pull off. Reassembled and test-spun: first time the motor wasn’t seated and two screws were missing; after refitting, done. A quick comparison of the drills on hand: the brushless ones are very loud, the brushed one a bit better. The second pack gets the same treatment — the original cells were only 1300mAh, now 2500mAh.

Outcome

Steps8 steps · click a frame to jump

1. 
   1. Diagnosis: motor shorted and smoking, packs dead

   The whole drill set is dead; straight onto a DC supply, the back smokes as soon as it’s switched on, and inside the motor is shorted; the two packs were probably killed by the heavy current.

   00:01 – 00:31
2. 
   2. Pull the motor from an old Boda drill

   There’s an unwanted Boda drill on hand, already taken apart with the switch removed; the motor is good but slow, no high-speed gear; just right to pull the motor and replace the dead one.

   00:31 – 00:57
3. 
   3. Pick cells: 2500mAh 12C power cells, 12mΩ, three of them

   Do the battery first; 2500mAh 12C power cells with only 12mΩ internal resistance, three of them.

   00:58 – 01:09
4. 
   4. Original pack has many wires and a thermal cutoff: don’t strip it, weld in place

   The original pack is fairly complex, wires everywhere plus a thermal cutoff; too many wires, so don’t strip it fully for welding or you’ll lose track of which is which — weld straight over the original positions.

   01:09 – 01:28
5. 
   5. Compact welder on the nickel strip: it won’t pull off

   This nickel strip welds fine with this welder; the welder is compact, light and easy to carry; once welded it won’t pull off.

   01:28 – 02:12
6. 
   6. Reassemble and test: motor not seated, two screws missing, refit and done

   Repaired; the rear screws weren’t tight and two seem to have fallen out; the motor wasn’t seated properly before, fine after refitting.

   02:12 – 02:26
7. 
   7. Comparing drills: brushless is loud, brushed a bit better

   A look at the drills on hand: the brushless ones (two) are very loud in use, the brushed one is a bit better.

   02:26 – 02:58
8. 
   8. Second pack: 1300 → 2500mAh

   The second pack gets done too; for my own use I’ll obviously use the best cells; it only had 1300mAh inside, now 2500mAh.

   02:58 – 03:21

Bill of materials

Measured on camera

Creator’s tips

• Original pack with lots of wires and a thermal cutoff: don’t strip it fully, weld in place over the original positions so you don’t mix up the wires 01:17
• A cordless drill pulls heavy current — pick 12C power cells and check the internal resistance 01:04
• A good motor from an old tool can be pulled and reused 00:45

Pitfalls

• Motor not seated and two screws missing, had to refit once 02:18
• A shorted motor will wreck the packs with heavy current 00:19

Li-ion safety

• A dead tool smokes when powered — diagnose on a controllable DC supply 00:14

Quotes