New battery for a soldering iron
Creator’s own settings as stated in the video (timestamps link to the moment). Not official values — test on scrap first.
Bill of materials
Welder, accessories, consumables and parts used in this build; quantities and specs are editable Download BOMDescription
8 × Lishen 21700 pulled from floor washers (IR 9–10) as a new battery for a soldering iron: waterproof box is a fixed size so no holder, cells hot-glued, AWithZ H2 spot-welds the nickel strip, 14.43V after welding, BMS not arrived yet so only the + / − leads are soldered on
The soldering iron hasn’t been lasting lately, so a new battery from 8 × 21700 — Lishen cells pulled from floor washers and the like, IR around 9–10. Using the AWithZ H2 handheld spot welder; the strip cut in advance wasn’t enough, so more is cut; no holder, because the waterproof box is a fixed size and with a holder a battery this big wouldn’t fit, so the cells are hot-glued instead. Welding done, pack voltage measures 14.43V; old battery removed; the new BMS hasn’t arrived so it isn’t fitted yet, just solder on the two + / − leads. Comments ask whether the IR meter is any good and for a store link, and why not use fibre tape for a sturdier build.
Outcome
| Goal | New 21700 battery for a soldering iron |
| Build | 8 × Lishen 21700 salvaged cells, 4S2P (inferred), waterproof box |
| Result | 14.43V after welding, waiting on the BMS · verified on camera: 59–69s voltage measured at 14.43V |
Steps4 steps · click a frame to jump
1. 8 × Lishen 21700 salvaged cells, IR 9–10The soldering iron doesn’t last; Lishen cells pulled from floor washers and similar, IR around 9–10.
00:00 – 00:22
2. H2 spot welding; hot glue instead of a holderAWithZ H2 handheld spot welder; the pre-cut strip isn’t enough, cut more; hot-glue the cells, because the waterproof box is a fixed size and a holder wouldn’t fit; spot-weld the pack.
00:28 – 00:55
3. 14.43V after welding, remove the old batteryWelding done; pack voltage measures 14.43V; take out the old battery.
00:59 – 01:09
4. BMS not here yet, solder the + / − leads for nowThe new BMS hasn’t arrived so it isn’t fitted; just solder on the two + / − leads.
01:14 – 01:22
Bill of materials
| Lishen 21700 salvaged cells ×8 | IR 9–10 · Battery replacement |
| AWithZ H2 handheld spot welder ×1 | Spot welding |
| Nickel strip | Connections |
| Hot glue | Holds the cells instead of a holder |
| Waterproof box ×1 | Fixed size · Enclosure |
| IR meter / multimeter | Measurement |
Measured on camera
| Cell internal resistance | 9–10 mΩ 00:14 |
| Pack voltage | 14.43 V 00:59 |
Creator’s tips
- When the enclosure is tight, skip the holder and hot-glue the cells 00:42
- Test IR on salvaged cells first (9–10 is usable) 00:14
Pitfalls
- Pre-cut nickel strip ran short, had to cut more on the spot 00:28
- BMS not arrived, no protection for now 01:14
Li-ion safety
- Using it without a BMS is risky; one is on the way 01:14
