I think you're going to need tabs of some sort to maintain the electrical connection between the battery and the rest of the game. What I would recommend doing is buying a new battery that comes with tabs attached (that's what I did, though I never got around to installing it, so I haven't tested it myself). There are a number of sellers that provide the batteries with tabs, and although it's more expensive that way, it's the better option overall. I think what you'll need to do is (a) remove the old battery and the old solder tabs, (b) place a new tabbed battery into the place where the old one went, and (c) solder the edges of the tabs to the motherboard. This way, you won't have to solder anything to the battery itself (which can cause the battery to explode), and you'll be able to reestablish the old connections and get a saving game.
