Does Soldering Damage Cells? 3 Alternatives to Spot Welding
When connecting 18650 battery cells, the most common method is soldering. But you've probably heard the warnings — "Don't solder on cells," "Soldering causes explosions." Are these claims true? If so, what are the alternatives? In this post, we’ll explore the real risks of soldering and walk you through three safe ways to connect lithium cells without using a spot welder.
Why is Soldering Considered a Problem?
Soldering involves applying heat to melt the solder onto a connection. The problem lies in that very heat. 18650 lithium-ion cells are highly sensitive to temperature, and anything over 60°C can start to break down the internal electrolyte. Improper soldering can cause the following issues:
- Gas Expansion: Excessive heat causes the electrolyte to vaporize, increasing internal pressure and potentially swelling or leaking.
- Reduced Capacity and Lifespan: Heat stress deteriorates cell performance and lifespan.
- Fire Hazard: Damaged insulation could result in internal shorts and thermal runaway.
So it’s not soldering itself, but how the soldering process impacts the cell thermally that creates the danger. What can we do instead?
Alternative #1: Clamp Contact (Compression)
This method uses physical pressure to hold a nickel strip against the cell terminal without applying heat. The structure is simple—place the strip on the terminal and use a clamp, screw, or spring to apply pressure.
- Pros: No heat, reusable, easy to assemble and disassemble
- Cons: Requires careful mechanical design, potential contact resistance
This approach is widely used in prototypes or modular designs and is growing in popularity through DIY communities using neodymium magnets for contact pressure.
Alternative #2: Dedicated Cell Holders
Plastic holders with built-in terminals allow easy plug-and-play battery connections. Just slide the cell into the holder, and metal contacts align with the terminals automatically.
- Pros: Easy for beginners, no soldering or welding, safe handling
- Cons: Limited current capacity, can be sensitive to vibration
Ideal for LED projects, sensors, or educational kits. However, not suitable for high-drain applications like power tools or large packs.
Alternative #3: Capacitor Discharge Spot Welder
Spot welding briefly applies a high current pulse to fuse metals together. A capacitor discharge welder stores energy in capacitors and releases it in a burst, powered by a 12V battery.
- Pros: Minimal heat exposure, fast and strong welds
- Cons: Requires circuit building knowledge, careful component selection
Using basic parts like an NE555 timer or IRF3205 MOSFET, you can DIY your own compact and affordable spot welder. It’s a common method among experienced battery builders.
Recommended Combo: Light Solder + Clamp or Magnet
Combining methods offers the best results. A 1-second light solder with a clamp or bolt adds strength and reduces risk. Or use a cell holder with magnetic contacts for improved pressure and reliability.
Conclusion: Soldering Isn’t the Enemy—Heat Is
Saying “soldering kills cells” is only half true. It’s excessive or prolonged heat, repeated soldering, and lack of thermal awareness that actually damage the cell. If a spot welder isn’t an option, one of these three methods—or a hybrid—can still ensure safe, durable connections.
Even without fancy equipment, what matters most is protecting your cells and ensuring long-term performance. Choose the method that best suits your application, skill level, and safety needs.