I want to fix Christmas lights like these, whose wires got cut near the batteries. The LEDs near the batteries still work.
I tried touching the wires from the two parts and I was surprised that the they seem to have metallic insulation. I sliced one LED at the end and confirmed that touching the inner rods does turn this LED on. Here is a picture of the two pairs of wires I want to solder:
The outside of the wires has a silver color, the inner rod looks like copper.
What is the name of this type of insulated wire, and how to solder it back together?