If you are talking about it sitting for a couple of weeks, it should be no issue. But to ease your mind (1) go for a nice drive until all of your temps (water and oil) are at normal operating temperatures every week or so, or (2) get a well reviewed battery maintainer like a CTEK
https://insight.daumphotography.com/...e-out-of-this/. Be sure that the maintainer has an AGM setting, since that cycle is a bit different than standard lead acid car batteries. Our X3s come with a AGM from the factory. Use the positive connector along with the ground stud, under the hood (passenger side of the engine compartment).
You can safely leave the CTEK maintainer connected for extended periods of time.
FWIW, what I would not do is simply idle the engine. This is really bad for the engine since typically the oil and coolant won't get hot enough, and you will end up with condensate and acids that don't burn off (as they do when you reach operating temperatures) and also remain in your oil and throughout your exhaust system.