hi thanks for the input,but batteries that are in packs hve tags welded onto them and the welded straps are only attached by a tiny spot weldd ,so the weld only requires a fraction of a second or so there is no overall heating of the cell .i have used the full sized spot welders ,and even they only take seconds to weld depending on the gauge of the metal. I think that a brass or copper bit would be needed and with a very narrow flat point on it.what i need is the size of transformer and size of the points .one idea that i am toying with is a ring that goes round the tip and is placed on the terminal that the tip and comes through and welds the strip.