Not trying to be patronising but you do know the transponder chip and the electronics with the battery are separate parts?I had to do this at the weekend - was putting it off as the key had been absolutely buried in superglue by the previous owner. But the battery was dire and I've not managed to program the right replacement fob yet.
Similar story that the blade was a glued/integrated one Vs the spare fob, luckily I had the blade cut for the new fob already. So just switched the electronics after some chisel and knife antics.