Hmmm so soldering on to batteries is kinda hard. The problem is that they absorb the heat so fast your solder wont melt. And if it takes you a long time, you could damage the battery.
The trick is to turn your soldering heat up really high so you can melt the solder before the heat dissipates. Coating it with lots of flux is also good. If you dont have a good soldering iron perhaps you should take ed's suggestion . . .
You probably also should practice soldering wires onto thick peices of metal first just for practice . . .