also for thicker material i use always 1,6mm sticks, i think, thicker sticks is not so good for the battery plates, with 1,6 sticks i have longer time current from the battery…
i give more current on the regulation spiral wire, but weld only a half stick lenght, then i stop for a moment and the stick can cool down ,so with the 1,6 stick and strong current i can weld also thicker metal..
the whole system 36 volt - batteries in serie, loaded up with fotovoltaic and wind with 12 v
important is a good strong connection on the battery poles, otherwise the can melt away…
before i found the spiral resistance, i welded alwas in steps of some centimeters only to avoid overheating of the sticks, this works also fine,otherwise the sticks can become too hot and melt on the stick holder and fall down —happened when i was a beginner..