Your owner's manual outlines how to change the battery in your smart key; and indicates replacement batteries are available at your Jaguar dealer. They are also available at RadioShack for about $6.

The manual directs one to pry off the chrome ends of the smart key using a small screwdriver. Let me add that the screwdriver must be very, very small to reach into the leverage point. It helps to use a jewelers loupe and bright lighting.

The emergency key is held into the smart key by a plastic locking tab, which can break with time and use. Then the smart key will no longer "hold" the emergency key, our key ring, etc.

You can "fix" your smart key without buying a new smart key. The "black half of the smart key contains the circuit board, and this portion does not need to be replaced. You can fix the broken tab by merely purchasing the "button half" of the smart key, which contains the holding tab. These half keys are available on eBay. Just remove and replace the button half, leaving the black half in place. No reprogramming is necessary.

However, if it appears that new battery, etc. does not fix your smart key, you still have the option of buying a new smart key on eBay. Buy one without the emergency key, so you can use your old emergency key.

I have not verified this, but eBay sellers of smart keys say smart keys can be reprogrammed by some locksmiths, as an alternative to your Jaguar dealership.