Ep. 30 | One video teaches you how to build a 21700 pack — never worry about long-range battery again

Hands-on 21700 pack for FPV long-range / goggle power: nickel + copper strip about 0.3mm at gear 25, fish paper, weld + and − separately, balance lead, then fibre tape + flame-retardant foam + heat-shrink

Field battery boxes, long-range packs and goggle batteries for FPV quads are all 21700 NMC inside; if you can build your own you save money for other parts. Tools: 21700 cells, a cell holder, nickel strip, copper strip, heat-shrink and a spot welder — a soldering iron can hardly get nickel strip to hold, and poor temperature control raises the internal resistance. The creator uses an AWithZ machine that welds nickel strip or 0.15mm copper strip with ease, max gear 99; the nickel + copper combination of about 0.3mm is usually around gear 25. First stick fish paper on the cell to insulate the outer rim; when welding, one pen presses the strip down while the other welds; on the other side, weld + and − separately — never weld them together; solder the balance lead and power lead to + and − (red positive, black negative); wrap in fibre tape, add flame-retardant foam, slide on heat-shrink, and a goggle battery is done. Reminder: lithium batteries are flammable and explosive, so take extra care while building.

Outcome

Steps6 steps · click a frame to jump

1. 
   1. Background: field boxes and long-range packs are all 21700

   Field battery boxes, long-range packs and goggle batteries are all 21700 NMC inside; many people buy factory-made ones, but building your own saves money for parts; the method is the same for all of them.

   00:00 – 00:34
2. 
   2. Tools, and why a spot welder

   21700 cells, a cell holder, nickel strip, copper strip, heat-shrink and other consumables; the spot welder joins cells in parallel / series with nickel strip; a soldering iron can hardly hold, and poor temperature control raises the cell’s internal resistance.

   00:34 – 01:08
3. 
   3. Machine and gear: AWithZ, 99 gears, about gear 25 for the 0.3mm combo

   Long-established maker AWithZ, welds nickel strip or 0.15mm copper strip with ease; cut the strip to size and fix the cells in the holder; set the gear by strip thickness, max 99; nickel + copper at about 0.3mm is usually around gear 25.

   01:08 – 01:29
4. 
   4. Fish paper, press with one pen and weld with the other, keep + and − apart

   Fish paper on the cell insulates the outer rim; one pen tip presses the strip down, the other welds; on the other side weld + and − separately — never weld them together or it shorts.

   01:29 – 01:47
5. 
   5. Solder balance lead and power lead, wrap it up

   Solder the balance lead and power lead to + and −, red positive, black negative; wrap in fibre tape, add a layer of flame-retardant foam, slide on heat-shrink — the goggle battery is done.

   01:47 – 02:06
6. 
   6. Reminder: lithium batteries are flammable and explosive

   Not hard to build, provided you have a good spot welder; lithium batteries are flammable and explosive, so take extra care while building.

   02:06 – 02:19

Bill of materials

Creator’s tips

• Set the gear by strip thickness; nickel + copper at about 0.3mm uses around gear 25 01:19
• One pen tip presses the strip down, the other welds 01:33
• A soldering iron can hardly hold on a cell and wrong temperature raises internal resistance — use a spot welder 00:57

Pitfalls

• Weld + and − together and it shorts (the video shows what happens) 01:40

Li-ion safety

• Fish paper insulates the outer rim of the cell 01:29
• Lithium batteries are flammable and explosive; take extra care while building 02:10

Quotes