808 posts · Joined 2008. #6 · Dec 30, 2017. If you replaced the main battery, as others have said you need REGISTRATION, not coding. Even if that wasn't the cause of the message, you've swapped it out now so registration should be done. The replace key fob/remote battery message is pretty clear that it means the fob. If you change either of those specs, you need to program the car for the correct capacity, and then register. Registering the battery does a few things: 1) Tells the car a new battery has been installed. 2) Records Mileage. 3) Records battery condition (voltage, charge level, etc) at 80% capacity to base the charging profile off of. The only key that now still works, with some difficulty, is the old one I am trying to replace, be it with a different battery than it had before I started experimenting with this. The keys seem to all the same inside, except for a figure on the inside of the cover, which looks like a clock dial with an arrow going through it, e.g. from 3 to 9 The only way is to cut it open and then solder the new battery and glue the remote back on. Also the newer diamond shaped keys dont come apart that way. They use a lithium rechargeable that is not meant to be replaced. If it fails you either have to cut the key apart to replace it or buy a new key. Plug the BMW scan tool into this port. Note that generic OBD2 scanners are unable to perform BMW battery registration. Turn Ignition on: Turn the ignition key to option II. For models with a Push Start button, press it a couple of times and avoid pressing the brake pedal when you press the start button. For non-comfort-access key fob, the battery is soldered inside the fob. You will have to carefully cut the two halfs with a knife and then desolder the battery; then, resolder the new battery. Save yourself the trouble and give the dealership your VIN and proof of reg, and have them order you a new key. in this video I show you how you can program keys very easily using the newest method which is the key reader now years ago when this all started this was ne Got a new key and don’t know how to program it for your BMW? Today, CJ will show you how to do it in seconds in your F Series BMW!Read more about key fob re xqEGNZj.