Nickel Strip vs Copper Strip for Battery Packs: What You Need to Know
Why Your Tab Material Choice Matters More Than You Think
The interconnect material in your battery pack is a significant part of the pack's total internal resistance. This matters because every milliohm of resistance in your pack's current path generates heat during discharge and reduces the energy that actually reaches your load.
For a low-drain pack (a power bank, a flashlight, a small solar storage device), this doesn't meaningfully affect pack performance — the currents are small enough that strip resistance is negligible compared to cell internal resistance.
For a high-drain pack (an e-bike motor pulling 20–50A continuously, a power tool, a racing EV), the strip material becomes a real variable. The difference between 0.15mm pure nickel and a double layer of 0.15mm nickel-plated copper on a 30A continuous load is measurable in watts of heat generated and in pack temperature under load.
The other reason this matters: getting it wrong costs cells. Nickel-plated steel — which looks identical to pure nickel strip and is commonly sold as a cheaper alternative — has significantly higher resistivity and causes pack heating problems that destroy cells. Knowing how to identify what you're buying matters as much as knowing which material to buy.
Watch this comparison of nickel and copper strip for battery pack building:
What Is Pure Nickel Strip?
Electrical Properties
Pure nickel (99%+ purity) has an electrical resistivity of approximately 6.99 × 10⁻⁸ Ω·m (69.9 nΩ·m). This is significantly higher resistivity than copper (16.8 nΩ·m) — nickel is approximately 4× more resistive than copper on a like-for-like basis.
In practical strip terms for 8mm wide, 0.15mm thick pure nickel:
- Resistance per metre: approximately 0.58 mΩ/cm (5.8 mΩ per 10cm)
- For a typical bracelet cell group strip run of ~80mm: approximately 0.46 mΩ
This becomes relevant at high current. At 20A continuous through this strip: power dissipated = I²R = 400 × 0.00046 = 0.18W per strip section. On a pack with 10 series groups at 20A: significant cumulative heating.
Weldability
Pure nickel is the easiest battery tab material to spot weld. Its resistivity is in the range where standard mid-range bench welders (Sunkko 737G+, K-Weld) and professional CD systems all produce reliable welds without special electrode materials or abnormally high energy settings.
The nickel strip's resistance is high enough that current concentrates at the nickel-to-cell-terminal interface (the highest resistance point) rather than flowing away through the strip, which is exactly what you need for a good weld. The metallurgical compatibility between nickel and steel cell terminals is also excellent — weld quality is consistent and predictable.
Where Pure Nickel Excels
- Standard 18650/21700 pack assembly for applications up to moderate current
- Any builder using a mid-range transformer welder — the welding parameter space for pure nickel is wide and forgiving
- Corrosion resistance — nickel forms a stable, thin protective oxide that doesn't significantly increase resistance over time or in humid environments
- Cost effectiveness — pure nickel strip is affordable and widely available
Limitations
- Higher resistivity than copper — at high continuous currents (25A+), the strip resistance creates meaningful heat. For high-drain applications, you need either thicker nickel, double-layer nickel, or copper.
- Current density limits — a single layer of 0.15mm nickel strip has a practical continuous current limit of approximately 10–15A before heat becomes a concern at the strip itself
- Not infinite scalability — stacking multiple layers of nickel adds complexity; at some point copper makes more sense for high-current bus connections
What Is Nickel-Plated Steel Strip?
How It Differs from Pure Nickel
Nickel-plated steel is a steel substrate with a thin nickel electroplating on the surface. From a visual inspection, it looks essentially identical to pure nickel strip — the same silver-grey colour, the same form factor. The difference is in the bulk electrical properties.
Steel has a resistivity of approximately 100–130 × 10⁻⁸ Ω·m — roughly 15–20× higher than pure nickel and 60–80× higher than copper. A strip that is 95% steel with a thin nickel coating has electrical resistance much closer to steel than to nickel.
The nickel-plated steel strip on the market is typically specified for "spot welding nickel strip" — which is accurate in the sense that you can weld it. What the listing often doesn't clarify is that it's not appropriate as a current carrier for serious battery packs.
Why It Is Cheaper
Steel is significantly cheaper than nickel. A roll of nickel-plated steel strip costs considerably less than the equivalent weight in pure nickel. For suppliers who don't identify their product clearly, this creates an opportunity for mislabeling — knowingly or unknowingly.
Nickel-plated steel is a legitimate product for specific applications (tab welding in low-drain consumer electronics, practice welding, certain industrial fastener applications). It's sold as "nickel strip" because it is nickel-surfaced. The problem is when it ends up in battery packs intended for serious current loads.
When to Avoid It
For any battery pack application with continuous discharge above 5–8A, or any pack where heat management is a concern: avoid nickel-plated steel entirely. The resistivity difference between nickel-plated steel and pure nickel is large enough to cause significant pack heating on e-bike packs, power tool packs, and similar applications.
How to identify nickel-plated steel: A magnet. Pure nickel is not ferromagnetic — it is not attracted to a magnet (or only very weakly). Steel is strongly ferromagnetic. A simple rare-earth magnet held near your strip will clearly distinguish the two. If your "nickel strip" sticks to a magnet, it's nickel-plated steel.
This test should be performed on every new strip purchase, particularly from unfamiliar suppliers or when the listing doesn't specifically state "pure nickel."
What Is Copper Strip?
Why Copper Has Higher Conductivity
Copper's electrical resistivity is approximately 1.68 × 10⁻⁸ Ω·m — roughly 4× lower than pure nickel. This means for the same strip dimensions, copper carries 4× more current at the same voltage drop (or equivalently, a copper strip generates 4× less heat than nickel at the same current).
For high-drain applications where every milliohm matters, this is the fundamental reason copper is worth considering. An 8mm × 0.15mm copper strip has approximately 1/4 the resistance of the same dimensions in pure nickel.
Current capacity of 8mm copper strip (continuous, conservatively):
- 0.15mm thick: approximately 25–35A
- 0.2mm thick: approximately 35–50A
- 0.3mm thick: approximately 50–70A
The Weldability Challenge
Copper's high conductivity is also the reason it's difficult to spot weld. Resistance welding works by concentrating current at the highest-resistance point (the strip-to-terminal interface) until that point reaches fusion temperature. With copper, the high conductivity rapidly carries heat away from the interface — meaning the energy you deposit at the interface doesn't stay there long enough to create a weld nugget, it disperses throughout the strip and cell.
Standard transformer welders (Sunkko 737G+, similar bench units) typically cannot reliably weld pure copper. The supercapacitor K-Weld can achieve copper welds with tungsten electrodes and optimal conditions, but results are inconsistent.
Reliable copper tab welding requires a professional capacitive discharge (CD) system with sufficient joule capacity and tungsten electrodes — typically a Sunstone CD200DP or CD400DP class machine. The CD welder's very high instantaneous peak current (even in a brief millisecond pulse) can deposit energy at the interface faster than copper can conduct it away. For a detailed explanation of why CD welding works for copper where transformer welding doesn't, our what is a CD spot welder guide covers the physics.
When Copper Is Worth the Effort
Copper is worth the additional equipment requirement and welding difficulty for:
- High-drain e-bike and EV packs drawing 30A+ continuous
- Bus bar connections — the main series connection strips that carry the full pack current
- High-performance power tool packs where pack heating is a real performance limitation
- Builders who already have a professional CD welder for other reasons and can access copper welding without an additional equipment investment
For most hobbyist 18650 builds running 15–20A continuous: stacked double-layer pure nickel is usually a more practical approach to increasing current capacity than switching to copper.
Head-to-Head: Nickel vs Copper for Battery Tabs
Conductivity and Current Capacity
| Material | Resistivity (nΩ·m) | Relative resistance (vs copper) | 8mm × 0.15mm continuous current |
|---|---|---|---|
| Pure copper | 16.8 | 1× | ~25–35A |
| Pure nickel | 69.9 | 4.2× | ~10–15A |
| Nickel-plated steel | ~1,000+ | 60× | ~3–5A only |
The current capacity figures are conservative continuous ratings before the strip itself becomes a heat source. Momentary/peak current can be higher.
Ease of Welding
Pure nickel: Easy. Any mid-range bench welder handles it. Wide parameter window. Predictable results.
Copper: Difficult. Requires professional CD system and tungsten electrodes. Narrower parameter window. Requires more calibration.
Nickel-plated copper (copper with nickel surface): Intermediate — the nickel surface provides a weldable interface while the copper core carries current. Better weldability than pure copper; better conductivity than pure nickel. More expensive and less widely available than pure nickel strip.
Heat Generation in the Pack
At 20A continuous through a single strip run:
- Pure nickel (0.15mm × 8mm): ~0.18W heat generated per strip section
- Pure copper (0.15mm × 8mm): ~0.04W heat generated per strip section
Over a 10S4P pack with multiple strip sections: the heat difference between nickel and copper is meaningful for packs running sustained high current. Nickel packs in high-drain applications run noticeably warmer at the strip level than copper packs. Over time and charge cycles, this differential heating accelerates cell degradation in the groups with the hottest strips.
Cost
Pure nickel strip: widely available, modest cost. Approximately $5–$20 for a 1m × 25mm roll at 0.15mm thickness depending on supplier.
Pure copper strip: slightly to moderately more expensive than nickel strip of equivalent dimensions.
Nickel-plated steel: cheapest of the three — which is why it shows up in low-quality listings.
Availability
Pure nickel strip: widely available from battery supply specialists, Amazon, and electronics distributors. Quality varies — use the magnet test on any new purchase.
Copper strip in battery-appropriate gauges: available from battery building supply specialists and copper strip suppliers. Less ubiquitous than nickel.
Nickel-plated copper: specialist battery supply distributors. Less common.
Which Welder Do You Need for Copper Tab Welding?
Why a Budget Welder Will Fail on Copper
A rechargeable handheld welder ($30–$150) or mid-range transformer welder (Sunkko 737G+ class) cannot reliably weld pure copper strip to battery terminals. The fundamental issue is energy delivery rate, not total energy: the weld interface needs to reach fusion temperature before copper conducts the heat away. Transformer welders simply can't deliver sufficient instantaneous peak current fast enough.
Specific failure modes with budget welders on copper: surface arcing rather than interface welding (the arc forms at the electrode tip rather than the strip-terminal interface), weld spots that look good but peel off cleanly, excessive strip surface damage without corresponding weld penetration.
The K-Weld (supercapacitor-based) achieves better results than transformer welders on copper with tungsten electrodes, but results are still inconsistent and are not a documented capability.
What the Sunstone Advanced Bundle Unlocks
A professional CD dual-pulse system like the Sunstone CD200DP or CD400DP provides:
- Sufficient instantaneous peak current (thousands of amps delivered in milliseconds) to overcome copper's thermal conductivity
- Tungsten electrode compatibility for copper welding
- Digital joule control for precise calibration of copper weld settings
- Dual pulse to condition the copper oxide surface before the fusion pulse
For builder who want to use copper tabs but don't have a professional CD welder: the nickel-copper sandwich method (below) is a practical alternative using standard nickel welding equipment. For a full guide to choosing a spot welder at each tier, see our how to spot weld battery tabs guide.
The Nickel-Copper Sandwich Method
How It Works
The nickel-copper sandwich bonds a copper strip between two layers of nickel strip, using the nickel layers as the weldable surface while the copper core carries the current.
Process:
- Weld a layer of pure nickel strip to the cell terminals as normal
- Place the copper strip on top of the welded nickel layer
- Weld a second layer of pure nickel on top of the copper strip, through the copper to the nickel below
The welds connect nickel-to-nickel through the copper layer. The copper is mechanically captured between the nickel layers without requiring a direct copper weld. Current flows through the high-conductivity copper core; the nickel layers handle the weld mechanics.
When to Use It
This method works well for bus bars and series connections — the strips that carry the full pack series current and therefore most benefit from copper conductivity. It's less practical for the individual cell-level connections within a parallel group (where you're welding many short strip sections to individual terminals) — those individual connections are better left in pure nickel.
The sandwich approach lets you get 80% of copper's conductivity benefit at the high-current bus connections using standard welding equipment, without needing to weld copper directly. It's a practical compromise for builders who have a mid-range bench welder and don't want to invest in professional CD equipment.
What Thickness Should You Use?
Strip Thickness by Application
| Application | Recommended strip | Notes |
|---|---|---|
| Low-drain hobby pack (under 10A) | 0.1mm pure nickel | Single layer; fine for flashlights, power banks |
| Standard 18650 e-bike pack (10–20A) | 0.15mm pure nickel | Most common choice; may double-layer at high end |
| High-drain e-bike (20–35A) | 0.2mm pure nickel or double 0.15mm | Double 0.15mm is easier to weld on standard machines |
| Very high drain (35A+) | Copper or nickel-copper sandwich | Requires professional CD system for direct copper welding |
| Main bus bar / series connections | Double nickel or nickel-copper sandwich | The full pack current flows through these; prioritize low resistance |
Current Capacity Reference Table
These are approximate continuous current ratings per strip section, based on strip self-heating as the limiting factor. Actual limits in a specific pack may be higher or lower depending on ventilation and thermal mass.
| Material | 0.1mm × 8mm | 0.15mm × 8mm | 0.2mm × 8mm |
|---|---|---|---|
| Nickel-plated steel | 2–4A | 4–6A | 6–8A |
| Pure nickel | 5–8A | 10–15A | 15–20A |
| Pure copper | 15–20A | 25–35A | 35–50A |
Note: double-layer stacking approximately doubles the current capacity for either material, at the cost of additional welding steps and strip thickness.
Which Should You Start With?
For most battery builders starting out: 0.15mm pure nickel strip. It's the right choice for the majority of 18650 and 21700 pack builds, it welds reliably on mid-range equipment, it has adequate current capacity for most hobbyist applications, and it's easy to source with confidence using the magnet test.
Upgrade to copper (or nickel-copper sandwich) when:
- Your pack's continuous discharge current exceeds 25–30A and your nickel strips are noticeably warm under load
- You're building a professional-grade e-bike or EV pack where every milliohm matters for range and pack temperature
- You have (or are acquiring) a professional CD spot welder that handles copper
Always verify that what you're buying is pure nickel, not nickel-plated steel. The magnet test is quick, free, and potentially saves your cells from early failure due to resistive heating from substandard strip.
For the complete step-by-step build process that puts strip selection in context, our how to build a battery pack guide covers the full assembly from planning to testing. For specific welding technique for each strip type, our how to spot weld battery tabs guide covers settings, electrode placement, and the pull test.
Frequently Asked Questions
What is the difference between nickel strip and nickel-plated steel for battery packs?
Pure nickel strip (99%+ nickel) has a resistivity of approximately 69.9 nΩ·m. Nickel-plated steel has a steel substrate with much higher resistivity — approximately 100–130 × the resistivity of copper, compared to nickel's 4×. For a battery pack, this difference translates directly into heat generation under load. At 20A continuous, a nickel-plated steel strip generates 15–20× more heat per metre than the same dimensions in pure nickel. You can tell them apart with a magnet: pure nickel is non-magnetic; steel is strongly magnetic. Always test any "nickel strip" purchase with a magnet before using it in a battery pack.
Is copper strip better than nickel strip for battery packs?
Copper is better than nickel purely on electrical performance — it has approximately 4× lower resistivity, meaning lower resistance, less heat generation, and higher current capacity per strip section. However, copper is substantially harder to spot weld reliably and requires a professional capacitive discharge welder with tungsten electrodes. For most DIY builders, 0.15–0.2mm pure nickel strip (or double-layer nickel) is the right choice because it's weldable on mid-range equipment and adequate for most applications. Copper becomes worth the added equipment complexity for packs drawing 25A+ continuous where strip heating is a real performance concern.
How thick should nickel strip be for an e-bike battery?
For a standard e-bike pack drawing 15–25A continuous: 0.15mm pure nickel strip is the minimum; 0.2mm or double-layer 0.15mm is more comfortable for consistent performance. For packs drawing 25A+: double-layer 0.2mm nickel or a nickel-copper sandwich at the main series connections. The strip thickness selection is about matching current capacity to your peak and continuous discharge requirements with reasonable thermal margin. A single layer of 0.15mm nickel strip handles approximately 10–15A continuous before becoming a meaningful heat source; this is adequate for moderate e-bike packs but limiting for high-performance builds.
Can you spot weld copper strip with a regular spot welder?
Not reliably. Standard transformer-based bench welders (Sunkko 737G+, similar) typically cannot weld pure copper because copper's high electrical conductivity dissipates heat faster than the transformer welder can deposit it at the weld interface. A professional capacitive discharge (CD) system with tungsten electrodes and sufficient joule capacity is required for reliable copper tab welding. The alternative is the nickel-copper sandwich method, which bonds copper strip between two nickel layers using the nickel as the weldable surface — this works with standard nickel welding equipment and captures most of copper's conductivity benefit.
How do I know if nickel strip is pure nickel or nickel-plated steel?
Use a magnet. Pure nickel is not ferromagnetic — a rare-earth magnet will not stick to pure nickel strip (or only very weakly). Steel is strongly ferromagnetic. If your "nickel strip" is attracted to a magnet, it contains steel — either as a nickel-plated steel product or as a low-purity nickel alloy with significant iron content. Perform this test on every roll from any new supplier or any roll where the product listing doesn't explicitly state "pure nickel" with a purity specification. This takes 5 seconds and protects your cells from the resistive heating damage that nickel-plated steel causes in high-drain applications.
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