If it’s like stained glass, get a drop on your iron and touch quickly to the point you want to leave the dot. I wonder if you have to flux to get it to adhere? All I saw in another site was to file the battery top a bit.
Wish I knew the answers. That linked page mentioned fluxing. I do have a soldering iron out in the garage somewhere but my soldering experience is limited. I once had a box of light strips that came with the wrong plugs, whenever I replaced one I had to reuse the old plug and solder on the new wire. Didn't matter if it was a misshapen mess.
Might grab an old metal tin or a can or something and experiment. It sounds like fun actually. Wouldn't want to try it on a battery until I have some idea what's going to happen.