What Nickel Strip Size Do You Need? The Complete Battery Builder’s Guide
A beginner-friendly guide for DIY battery builders, power-tool pack rebuilders, and e-bike tinkerers.
Why Nickel Strip Size Actually Matters
When you’re building or rebuilding lithium-ion battery packs, the nickel strip is not “just metal.” It’s the highway that carries current between your cells. If the strip is too thin or too narrow, you get:
- Excess heat in the nickel
- Voltage sag under load (your tools feel weak)
- Early BMS cutoff or nuisance trips
- In extreme cases: burned nickel, melted insulation, or pack failure
In this guide, we’ll break down exactly what thickness and width of nickel strip you need for different types of packs: power-tool batteries, power banks, 1S–2S packs, and e-bikes.
Pure Nickel vs. Nickel-Plated Steel
Before we talk about thickness and width, we need to talk about the material itself. There are two main types of “nickel strip” you’ll see online:
- Pure nickel
- Nickel-plated steel
How to Tell the Difference
- Magnet test: pure nickel is weakly magnetic or not magnetic; nickel-plated steel grabs the magnet hard.
- Grind test: if you lightly grind the edge, steel underneath will show a different color/spark than nickel.
- Price and honesty: if it’s super cheap and not clearly labeled “pure nickel,” assume it’s plated steel.
For high-drain packs (power-tool batteries, e-bikes, high-performance builds), you should use pure nickel only. Nickel-plated steel has much higher resistance and heats up more.
If you don’t want to gamble on random online listings, you can find tested pure nickel strips and fish-paper insulators in our collection here: RenewSpark Nickel Strips & Fish Paper.
Step 1: Know Your Cell Current (Discharge Rating)
Your nickel strip has to safely carry the current of the parallel group. That depends on:
- The cell model
- The maximum continuous discharge rating
- How many cells are in parallel
Examples of popular 18650/21700 cells:
- Samsung 25R: ~20A continuous per cell
- Molicel P42A: up to ~45A continuous per cell (high-performance 21700)
- Molicel P50B: up to 60A continuous per cell (5.0Ah — the highest-current cell in the P-series)
If you have 3 cells in parallel (3P) and each cell can do 20A, that group could see up to 60A. Your nickel has to be sized to handle the worst-case current for that group.
Step 2: Real-World Current Ratings for Nickel Strip
Below is a practical, real-world guide for continuous current on pure nickel strip. These are conservative, everyday-use numbers (not “absolute maximums in a lab”).
Pure Nickel – Approximate Safe Continuous Current
| Nickel Size (thickness × width) | Approx. Max Continuous Current |
|---|---|
| 0.10 mm × 7–8 mm | ~8–10 A |
| 0.15 mm × 7–8 mm | ~12–15 A |
| 0.15 mm × 10 mm | ~15–20 A |
| 0.20 mm × 7–8 mm | ~20–25 A |
| 0.20 mm × 10 mm | ~30–40 A |
| 0.30 mm × 8–10 mm | ~40–60 A (requires a strong spot welder) |
If your strip is nickel-plated steel: as a simple rule of thumb, reduce those current numbers by about 50% because of higher resistance and heating.
Also remember: you can always increase current capacity by using:
- Wider nickel (10 mm instead of 7 mm)
- Multiple strips in parallel (e.g., “double-stacked” nickel on tool packs)
- Copper + nickel busbars for very high-power builds
Recommended Nickel Size by Application
Here’s where most builders just want a straight answer: what should I use for my pack?
1. Power-Tool Batteries (DeWalt, Milwaukee, Makita, etc.)
- Recommended thickness: 0.20 mm pure nickel
- Recommended width: 7–10 mm
- Why: Tool packs see very high peak currents (impact wrenches, circular saws, etc.).
- Many OEM and professional rebuilds use double-stacked nickel or multiple strips to share current.
2. Power Banks (USB output)
- Recommended thickness: 0.10 mm or 0.15 mm pure nickel
- Recommended width: 6–8 mm is usually plenty
- Why: Typical USB power banks only see 1–5 A total. There’s no need for thick, heavy strip.
- Thinner nickel is easier to weld with small hobby spot welders and keeps the pack compact.
3. 1S–2S Packs (DIY, Arduino, CCTV, LED, small robotics)
- Recommended thickness: 0.10 mm or 0.15 mm pure nickel
- Recommended width: 6–8 mm
- Why: These packs usually run small loads and don’t draw big continuous current.
- Perfect for small projects, test packs, and compact builds.
4. E-Bike Packs / High-Power Packs
- Recommended thickness: 0.20 mm or 0.30 mm pure nickel
- Recommended width: 8–10 mm (often multiple strips)
- Why: E-bikes can draw tens of amps continuously and even more in bursts.
- Many builders combine:
- Multiple nickel strips in parallel
- Nickel + copper (nickel only for the weld area, copper for bulk current)
You can find 0.1 mm, 0.15 mm, and 0.2 mm pure nickel, plus fish-paper insulators for pack ends and series connections, in our curated collection: RenewSpark Nickel Strips & Fish Paper.
How Wide Should Your Nickel Be?
Thickness gets all the attention, but width is just as important. Wider strip = more cross-section = lower resistance.
Simple rule of thumb:
- Each parallel group’s nickel should be sized for the maximum current that group might see.
- If you need more current capacity, you can:
- Use wider strip (10 mm instead of 7 mm)
- Use two strips side by side
- Use double layers (stacked nickel)
Rough guide:
- 5 mm wide: very low-drain (small power banks, signal electronics)
- 7–8 mm wide: common size for tool batteries and medium-drain packs
- 10 mm wide: better for high-current groups, e-bikes, and heavy loads
How Many Spot Welds Per Connection?
The nickel size is only half of the story. You also need enough good, solid welds at each cell terminal.
As a general guide:
- 0.10 mm nickel: 2 welds per side of each cell is usually enough.
- 0.15 mm nickel: 2–3 welds per side.
- 0.20 mm nickel: 4–6 welds per side (depends on welder power and weld size).
- 0.30 mm nickel: often 6–8 welds per side and a strong professional welder.
You should be able to tug on the strip and see the metal deform before welds pop off. If welds break too easily, your settings or electrode pressure may need adjustment.
Signs Your Nickel Is Too Thin or Undersized
Watch for these warning signs:
- Nickel strips feel hot under load.
- Noticeable voltage sag when you pull current (tool feels weak, e-bike slows fast).
- BMS cuts off early under load but seems fine at light load.
- Nickel turns dark, blueish, or discolored near high-current areas.
- Weld areas start to loosen, crack, or show heat damage.
If you see any of these, it’s a sign your pack design might need thicker or wider nickel, or multiple strips in parallel.
When to Use Copper + Nickel (Advanced)
For very high-current packs (for example, Molicel P42A builds, high-power tools, or powerful e-bike setups), 0.20 mm nickel alone may not be enough—especially over long runs.
One common trick is the copper + nickel sandwich:
- Use nickel directly on the cells (because it welds easily).
- Lay copper strip or busbar on top of the nickel to carry most of the current.
- Use a thin nickel layer over the copper if needed to weld and lock everything together.
This lets the copper do the hard work (low resistance, high current) while nickel stays in the weld zone where it’s happy.
Quick Cheat Sheet
- Power-tool packs: 0.20 mm pure nickel, 7–10 mm wide, often double-layered.
- Power banks: 0.10–0.15 mm pure nickel, ~6–8 mm.
- 1S–2S DIY packs: 0.10–0.15 mm pure nickel, ~6–8 mm.
- E-bike / high-power: 0.20–0.30 mm pure nickel, 8–10 mm, multiples strips or copper assist.
- Plated steel: avoid for high-drain; if you must use it, derate by ~50%.
Conclusion
Choosing the right nickel strip thickness and width is one of the most important parts of building a safe, reliable, and strong battery pack. Once you know:
- What cells you’re using
- How much current your pack needs
- Whether you’re building a low-drain or high-drain pack
…then picking the right nickel size becomes straightforward.
If you’re looking for tested pure nickel strips and fish-paper insulators for your next build, check out our selection at RenewSpark. We focus on DIY builders, power-tool rebuilders, and small pack projects, with fast U.S. shipping and high-quality materials chosen specifically for battery work.
