The problem (you can't buy one)
If your electronics workplace looks like mine when doing a project, you will know what chaos and cluttered means. This leads to other problems like the cable of my Weller soldering iron getting stuck and/ or intertwined with other cables and stuff just when you are trying to solder something - it sucks.
So for a long time I was looking for a really good LiIo or LiPo battery powered soldering iron. But as far as I could figure out there is none. I really don't now why but there is only crap with NiMn equipped soldering irons (alwas empty when you need them and no power to do real soldering work) or Gas powered soldering irons which lack adequate temperature setup and control.
So I started developing one when I found the Weller RT1 soldering tip. It has 40W power output and is capable of heating to the desired temperature within seconds (using the right power source and electronics).