Hi Adrian
Well. lacking a better idea, I put the charger on the terminal to the left of the battery one.
After a bit, the clicking stopped and I was able to unlock the whole car with the remote.
Batt now on charge. I was completely flaaaaaat., thus the relay clicking.
Something must have been left on I think- like you, I've left mine weeks before with no issues. Might be a duff batt'y. Hope not.
