All the E46 keys I've worked on did not need a new rechargeable battery. I took out the battery waited a while and put it back in and they magically started working again. Again I have yet to find a bad battery (remember the rechargeable batteries are only on the diamond shaped keys with no red light). There was one key that I repaired with a bad lock button which prevented it from reprogramming because the lock and unlock button are required. Replaced the tiny micro switch and got that key working. One key though I could not get to work at all. Buttons all tested good, battery was good, it just didn't work. Not sure about that one.
>Also, key still starts the car, just acts like the battery is dead.
That's not surprising since the key fob is not needed to start the car, that's the EWS transponder in the key which is totally separate.