I too have remote locking problems. When I bought the car one key didn't remote lock/unlock but started the car. Now my other key has gone the same way.
Tried charging up my previously good key by leaving it in the car in aux for 6 hours, still didn't work
So cut both keys open using method below. Then measured the unloaded battery voltage on both. Previously good one was 3.34V, the one that never worked 2.8V. Decided to replace the battery in the old one with a new battery.
The decided to re-initialise two different methods:
1 a. sit inside, close all doors
1 b. key in barrel move to pos 1 (aux) for a brief second or so
1 c. Press and hold unlock button and whilst doing so press the lock button three times
After 1 c. both doors should momentarily lock and then unlock signifying success. No such luck so tried:
2 a. key in and then rapidly switch to position and back 5 times
2 b. key in barrel move to pos 1 (aux) for a brief second or so
2 c. Press and hold unlock button and whilst doing so press the lock button three times
After 2 c. both doors should momentarily lock and then unlock signifying success. Again no such luck.
On one occasion I did get lock followed by unlock. But the key still didn't work. i also had weird things along the way like, on one occasion I opened the drivers door only to have the window lower fully, then when I closed it again it went back up again! It also stopped locking the petrol filler cap when locked from the door key, only the doors locked, although that seams to be OK again now.
I love my Z4 generally, love the looks, the handling the engine and all things mechanical. But the fickle electrical system is really getting me down! (constant intermittent airbag warnings, all different error codes, reverse sensors randomly working some times and just sounding continuous on other times)
If anyone has any ideas regarding the remote door locking, I would love to know.
MACK said:
raymond.harper said:
https://www.youtube.com/watch?v=e1o9vH3mgmg
+1
The battery itself about £5 from eBay etc. I done this repair 4 or 5 times for friends/family with E46 and it's pretty easy even for a novice. All you need is soldering iron and solder obviously.
Tried the spare key fob today, worked ok, went out for a drive for an hour, left it for half an hour or so, when I got back it wouldn’t open, had to use the key 
I read that it’s a fixed rechargeable battery, but some people have forced it open and replaced it, what are my options?