Like most people I don't have a welder so I started experimenting with using flux and other various agents until i finally found that filing the end of the battery would allow solder to pool. then I could solder a wire onto it easily.
This technique can be used for both normal and rechargeable batteries, so if you need to replace some rechargeable batteries in battery packs like the one from the Xbox 360 you can now do it. I also used it when making this instructable http://www.instructables.com/id/Copper-plating-made-easy/.
Comments are welcome and appreciated
Step 1: Materials
-A Soldering iron
-Some rosin core solder
-Two pieces of wire preferably red and black to avoid confusion
-Wire Strippers(not shown, but still needed)
-Some Skill with Soldering