Hi,
I replaced the battery on my 2006 x244 2.8JTD PVC about two years ago. On that occasion I unbolted the after market alarm unit and associated bonnet sensor, so as to clear the battery's exit path.
Read through the following procedure, and see if you still have a problem.
Minimum required tools are 10mm and 13mm spanners, but sockets with a short extension would make the task easier.
Unlike the x250 and later versions, there is no special procedure to be followed before disconnecting the battery negative.
Be aware of the potential hazards from sulphuric acid spillage, and with short circuits created by metal jewelry.
1. As the vehicle is a motorhome, remove all charging sources, by covering solar panels, and and switching OFF the mains charger.
2. Remove the battery negative connection. This should be a lever operated clamp at the front. It is a good idea to wrap the connector in a couple of plastic bags, to prevent accidental contact with the battery post. Also it helps to unclip the negative cable near the front of the battery, so that the cable can be pulled clear.
3. It may help at this stage if the heavy lead to unbolt the positive lead to the staarter. To access the starter connection press the two tabs on battery fusebox cover, and lift off. Using 10mm spanner or socket loosen the positive clamp at rear of inboard side of battery. Carefully lever off the clip that holds the battery fusebox to the battery. The fusebox can now be raised clear of battery top.
4. Using 13mm socket and extension, remove the clamping bolts and plates from the inner edge of the battery base.
5. Using the lifting cords, or handles fitted to the battery, raise the front end of the battery and slide it upwards and forwards over the front panel of the vehicle. As the battery is heavy, it may be safer if assistance is available at this stage. Lower the battery to the ground, or suitable support.
Replacement is generally a reverse of the removal procedure.
You will have to reset the clock on the instrument panel with the LHS button.
You may need to key a code into the radio to re-enable it.