⚠️ Important Safety Note

You are working with lithium-ion cells. A short circuit or overheating can cause fire or explosion. Only proceed if you are experienced with battery handling and have proper tools.

Never solder directly to the battery cell.

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🧰 What You Need

• 18650 flat-top battery (unprotected cell)
• Button top caps / nickel button caps (pre-formed)
• Spot welder (preferred method)
• Nickel strip (optional depending on cap type)
• Heat-resistant work surface
• Safety glasses
• Insulated gloves (recommended)

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🔧 Method 1 (Recommended): Spot Welding Button Caps

This is the professional and safest method.

Step 1: Inspect the Battery

• Ensure the 18650 cell is undamaged
• Check voltage is within safe range (typically 3.0V–4.2V)
• Clean the top terminal lightly (no grease or oxidation)

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Step 2: Position the Button Cap

• Place the button cap on the positive terminal (+ side)
• Ensure it is centered and flush
• Most caps are designed to “cup” the top of the battery

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Step 3: Prepare Spot Welder

• Set low-to-medium power (depending on nickel thickness)
• Use fine welding probes
• Test weld settings on scrap material first

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Step 4: Spot Weld the Cap

• Place nickel tab or cap contact points under the probes
• Apply 2–4 quick spot weld pulses
• Ensure firm mechanical bonding without overheating the cell

✔ Goal: strong bond without damaging the battery seal

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Step 5: Check Connection

• Gently tug to confirm the cap is secure
• Ensure no movement or loose edges

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Step 6: Repeat for Negative Side (if required)

• Most 18650 button caps are only used on the positive side
• If building a custom pack interface, repeat carefully on the negative terminal only if designed for it

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🔧 Method 2: Pre-Made Button Top Conversion Caps (No Welding)

Some caps are press-fit or crimp-style.

Step 1: Align Cap

• Place cap over positive terminal

Step 2: Press Fit

• Apply firm, even pressure
• Some designs lock mechanically without welding

⚠️ This method is less secure for high-current applications

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🔧 Method 3: Soldered Adapter (NOT Recommended for Cells)

Some DIY users solder a cap onto a nickel strip attached to the cell tab system—but:

❌ Never solder directly to the 18650 cell
❌ Heat damages internal chemistry

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📊 Best Practice Summary

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⚡ Professional Tip (Battery Builders Use This)

If you're building packs:

• It’s usually better to use nickel strips + spot welds rather than converting every cell to button top
• Button caps are mainly used for:
  • device compatibility
  • spring-contact systems
  • flashlight-style holders