tdm, Shonky is right, a 1/3 drop in voltage is unacceptable. If the voltage is less than ~2.7 under load, a signal is probably not even being produced. My O-Reilly's has a "key transmitter tester" tool that lights up when it detects a keyfob signal. You could see if a local car shop has that tool, but even so, the frequency might not be correct with so low of a voltage. If your key IS sending a signal but your car isn't unlocking, that's more proof that the battery is too weak.
I think you really need to replace the battery. One of the keys I've opened actually had a broken pin from the battery mount so it was obviously an open circuit, but another had a weak battery like yours, and replacing the battery fixed it. I agree that the shipping is high (you sound cheap like me!). I bought a few batteries on the last order, and have fixed two keys from it, so it helps spread the cost.
Another tip. I have learned the hard way to sand smooth the rough edges left by cutting open the key before gluing them back together. Two of the keys I fixed broke apart when their respective keychains were dropped on cement. Sanding the edges smooth and flat using a sandpaper block resulted in (so far) break-free repairs.
Finally, if your SO uses one of the keys you fixed, explain to (her) how to put the circuitboard back in the shell and tape/rubberband it in to get the car to start so she's not stranded if she drops it and it breaks when she's out.
dan in st. louis
01 e46 330i, 03 e46 330izhp, 06 X3, 88 (e30) 325is, 90 (e30) 325is