Flat battery

Any known causes for there to be a constant drain on the battery when key/ignition is off.
New to x19 ownership but also have a 126 bis. Cheers

God only knows but they all do it, I have a quick release on the battery

Hello martyn
A Lot is to do with the x19 having permanent live feeds to all their relays when the ignition is off
Most owners like myself connect the battery to a charger / monitoring system

There is a live circuit that goes to the car stereo/cigar lighter. Also there is a circuit for the parking lights and to bring the headlight pods down and finally the hot start fan on that blows on the carb.

Could be any of these, stereo, if you have one is a good place to start as they normally draw something to keep memory live.

You could try pulling fuses and see if that helps, if you can maybe measure to see what current is drawn at each fuse.

While mine is "resting" I disconnect the battery, but if I am driving it regularly it stays attached.

Good luck take you time and go with the approach that works for you.