Good afternoon Tom, in basic terms the battery monitor system does what it says and in certain conditions when the voltage is to low will send messages out which then in turn will put a display up on your touchscreen asking for certain stuff to turn off, also when the car is runing/driving it monitors and lets the relevent ECU know so that it can tell whether to put more charge into the battery or not.....also every now and then it will also instigate a calibration where it will bring the battery up to full charge when this is achieved it will bring it back down to ,i think from memory around 75% of the charge, once this is achieved goes back up to full charge, in saying all that it is dependent on how often the car is driven for the procedure to carry out the self calibration,meaning if only short drives are carried out it will take far longer to self calibrate than if your doing 100 miles each way on a singlr journey each day, so basicaly the monitor system needs to know when a new battery is fitted to calculate when to do all this, just so if you fit a battery in the morning it isn't gunner know and might start a calibration an hour later....
SDD is Jaguars diagnostic system or..... Symptom Driven Diagnosis-SDD this will be required to reset the monitor system but only if the battery is replaced for a new one.
I hope that spreads a little light on the system.
Respect
Dave