The TPS sensors have an on- board chip that directly senses pressure, temperature and centripital force. That isn't goinig to do you much good replacing the battery though.
Your idea of just pressing something metallic against each side of the battery will work OK but may be unreliable as others have pointed out.
You should not solder to any disposable battery, especially a lithium battery. It simply heats the battery too much. A much better way is to use a battery with spot welded tabs on it, and solder those tabs to the buss bars on the sensor itself. You can use standard tabbed batteries, band back the tab and solder a wire between the tab and the buss bar. A different way to go that works very well is to have someplace like Batteries Plus solder on tabs in a custom location (about 45 degrees apart, top vs. bottom) then trim the tabs to tuck down onto the buss bar ends, and finally just solder the tabs onto the buss bar ends. A very solid and safe method. I have done a few sets this way but unfortunately don't have photos (it was during tech day and things were a bit rushed). When I change tires this summer I will also install new batteries using that method and document it with photos for anyone else who wants to do his / her own that way.
Brian
I swear I did a search and did not come up with anything substantial. I just want an understanding how the tire pressure sensor internally works. Does it detect the amount of force being applied upon it? Basically how does it sense the pressure? The reason I am asking is I took the sensor out when I was changing my rear tire and wanted to change the battery. I got a new battery, but it is a PITA to solder a wire to the battery. So what I did is shown in the picture. It appears they fit fine, but wanted to put a rubber grommet on top and bottom to make sure enough pressure gets applied to the disc to make contact. If I do put rubber grommets, the encasing becomes tougher to shut. So was thinking perhaps I can press it in and just put tape around it (or secure it in some other means). But did not want that to cause issues with functionality.