Yes, you should register your battery. Some people say it's a "must" -- I agree with those that say "must".
If you can do coding, or have access to a coder, you can use INPA if your engine is listed there. If not, you can use EDIBIAS ToolSet 32 to register. (I had to do the latter for my E70 4.8i which was not listed in INPA.)
EDIT: I see Supercourse disagrees with me. I thought the X3's required registration too. I'll let someone else chime about X3's. Note that it's not related to AGM, gel, or wet cell batteries --- it's just the fact of having a new battery.
Last edited by brian5; 01-21-2013 at 12:02 PM.