This video shows how to change the battery in a Land Rover LR3 key fob. The LR3 key of this generation is rechargeable and is not changeable without cutting open the key fob and de-soldering the battery from the circuit board and then soldering in a new battery. If you do not have the tools or skills to solder in a new battery, you can take the circuit board and new battery to a camera repair or electronic repair shop. The cost to install a new battery should cost between $10 and $20.
The battery in the key fob has a life of 8 to 10 years, so if your original key fob has buttons that are worn out, then it would be prudent to change the battery at the same time.
You can use a precision circular cutting tool like a Dremel tool to cut the key case in half to expose the circuit board.
The Land Rover key uses a rechargeable VL2330 3V Lithium Coin Cell Battery that costs around $10: http://amzn.to/2grCJFV
The replacement Land Rover key shell can be purchased for around $10 : http://amzn.to/2zoOapo