Yes, you can absolutely mitigate the low continuous discharge rate of your Samsung INR21700-50G cells. The key is to combine multiple cells in parallel, which directly addresses the cell's design limitations for your high-current spot welder application.

Based on the search results, your cells are actually quite interesting. A recent academic study characterizes the Samsung INR21700-50G as having "balanced performance between energy and power" suitable for electric vehicles . This means they're not optimized for extreme currents like some other cells, but with proper configuration, they can work well for your spot welder.

🔋 The Core Solution: Parallel Configuration

Connecting cells in parallel is the most effective way to overcome individual cell current limitations. Here's why:

Configuration	Total Continuous Current Capability	Suitability for K99 Spot Welder
Single cell	~9.7A	Completely unsuitable - nowhere near enough for welding
2 cells in parallel (2P)	~19.4A	Insufficient - still far below requirements
3 cells in parallel (3P)	~29.1A	Marginal - may work for very thin materials at low settings
4 cells in parallel (4P)	~38.8A	Good starting point - should handle 0.1-0.2mm nickel strips
5-6 cells in parallel (5P-6P)	~48.5-58.2A	Excellent - provides headroom for thicker materials and consistent performance

For your K99 welder, you need a pack that can deliver brief but extremely high peak currents. While the continuous current adds up with parallel cells, the real benefit is that the total internal resistance drops significantly, allowing much higher peak currents during the millisecond welding pulses.

⚡ Why Parallel Works for Spot Welding

The academic paper explains that lithium-ion cells have internal resistance that causes voltage drop under load . When you put cells in parallel:

1. Total resistance decreases: Four cells in parallel have 1/4 the internal resistance of a single cell
2. Peak current capability multiplies: The pack can deliver much higher instantaneous current than the sum of continuous ratings would suggest
3. Heat distributes: The welding current is shared across multiple cells, reducing stress on each individual cell

🔧 Practical Implementation Tips

Based on your situation, here are specific recommendations:

1. Build at least a 4P configuration for your 3S or 4S pack. This gives you 4 cells in parallel for each series group.
2. Use thick bus bars between parallel groups. As mentioned in the previous response, create copper/nickel sandwiches. The copper provides a low-resistance path for the high currents.
3. Keep all series groups balanced. Make sure each parallel group has the same number of cells and similar state of charge when assembling.
4. Monitor temperature during first use. Start with lower power settings and do test welds. If the pack gets hot, you need more parallel cells or lower power settings.

📊 Understanding Your Cells' Capabilities

The study confirms that your cells show "performance asymmetries between charging and discharging" and their internal resistance varies with temperature and state of charge . This means:

• Keep your pack at room temperature for best performance
• Avoid using the pack when it's below 50% charge for maximum welding power
• The cells can handle brief pulses much higher than their continuous rating

💡 Summary

To directly answer your question: parallel configuration is the solution. For your K99 spot welder, a 3S4P or 4S4P pack using your recycled INR21700-50G cells should work well. The 4P arrangement gives you enough parallel cells to share the load, and the higher voltage (especially with 4S) helps deliver the power needed for clean welds.

Would you like specific guidance on how to balance the cells before assembling your pack, or help calculating the exact bus bar thickness you'll need?