Swapping a flashlight battery with a handheld mini Li-ion spot welder. The handheld mini welder is easy to carry and works for re-celling power banks, players and other small gadgets. Solder a Li-ion cell with an iron and the heat raises the pressure inside and can ruin the cell — only a spot welder will do

Flashlight 400mAh 14500 swapped for a 2000mAh 18650: handheld mini welder on 0.12 nickel strip — top gear punches through, gear 1 doesn’t hold, middle gear is right, don’t press hard

The flashlight dies in under two hours; opened up (pull forward, no screws) it turns out to be built cheap: a single 14500 400mAh NMC cell. He swaps in a 2000mAh 18650 that just fits. These cells are hard to solder (flux would help), so the creator first spot-welds a nickel tab on each end to try out the new mini welder (easy to carry, compact), in manual mode. 11 gears: top gear first to see its power — it holds firmly but punches two holes through the 0.12 nickel strip; then welded onto the cell it holds well. Thick strip takes the top gear, thin strip the middle; the higher the gear, the more power it uses. Gear 1 test: 0.12 strip peels off (not good), but very thin strip holds even on the lowest gear. Note: don’t force it down, keep the surface flat and just make good contact, or you’ll punch through. Cell swapped, OK.

Outcome

Steps7 steps · click a frame to jump

1. 
   1. Open the flashlight, find a 400mAh 14500

   The flashlight doesn’t last; easy to open, just pull forward, no screws; built cheap — a single 14500 400mAh NMC cell, no wonder it doesn’t last.

   00:01 – 00:55
2. 
   2. Swap in a 2000mAh 18650, just fits

   Found a 2000mAh cell; test-fitted, it just fits.

   00:55 – 01:09
3. 
   3. Hard to solder → weld a nickel tab on each end to try the new welder

   These cells are very hard to solder directly, flux can help; first weld a nickel tab on each end to try the welder; power on in manual mode; the little welder is easy to carry and compact and works fine; for small household cells and power bank re-cells you need a mini welder.

   01:09 – 02:14
4. 
   4. Top gear test: holds, but punches two holes

   If it doesn’t hold, change gear; first see what the top gear does: press and hold, the weld is firm, but it has punched two holes.

   02:14 – 03:02
5. 
   5. Weld onto the cell; gear vs strip thickness

   One weld on the cell, firm, it holds; the strip is 0.12; thick strip takes the top gear, thinner strip the middle; the higher the gear, the more power it uses; 11 gears in total.

   03:00 – 04:09
6. 
   6. Gear 1 test: 0.12 peels off, very thin holds

   On gear 1 the 0.12 strip peels off, not good, because the strip is fairly thick; very thin strip holds even on the lowest gear.

   04:09 – 05:09
7. 
   7. Key points: don’t force it, keep the surface flat; done

   Don’t force the pen down when welding — just punched through two more spots; keep the surface flat and make good contact; the welder is decent, link in the comments; cell swapped, OK.

   05:10 – 05:58

Bill of materials

Creator’s tips

• Thick strip on the top gear, thin strip on the middle; very thin strip holds even on the lowest gear; higher gears use more power 03:53
• Don’t force the pen down; a flat surface and good contact are enough, otherwise you punch through 05:12
• If a cell won’t take solder, use flux or just weld a nickel tab on 01:14

Pitfalls

• Top gear on 0.12 nickel strip punches two holes 02:54
• Gear 1 on 0.12 nickel strip peels off, doesn’t hold 04:24

Li-ion safety

• From the title: soldering a Li-ion cell with an iron overheats it, raises the internal pressure and can ruin it — only a spot welder will do

Quotes