Soldering a battery can be safe and easy
with a really good iron that combines:
- a fast regulation with a good thermal path between tip and heat element,
- enough heat power(80-150W)
- and enough mass to compensate the drop in heat when touching the cold parts
Surface preparation:
- cleaning surface with alcohol or very fine sanding
- adding flux
Adding the solder blob to the cell should take only 3-5 seconds at most
The temperature of the iron should be 350dC at most for lead solder, 400 for lead free
Let the cell cool and solder blob the next
Tin the copper sheet or wire
May add some flux to the copper sheet
Heat up the copper sheet or wire
Now stick the copper sheet with iron to the solder blob,
This should take only 2-3 seconds to melt the solder blob