Can a VL Calais with the injected Nissan 3.0-litre six-cylinder have a battery maintainer connected to the battery while the car has the positive and negative cables still connected. Some say it is better to leave the battery connected as computers may lose memory and the car may not idle correctly for a while and the engine will have to re-learn things as well as having the inconvenience of clock and radio memory being lost. Others say if the voltage goes a bit high from the charger it can damage alternator diodes or the alternator regulator. I have a solar panel that has 10-watt output and a built-in regulator. I have always removed cables on cars to be safe, but I do remember my 2001 Mitsubishi Verada computer did not like the battery being disconnected, as it had to learn how to idle again.
There shouldn't be any issue with leaving the maintenance charger connected to the battery, and other than the inconvenience if having to reset the clocks and radios there shouldn't be any issue caused by disconnecting the battery. After all you have to disconnect the battery when changing to a new one.