The battery does seem to deplete quicker than you might imagine, and I would say 4 weeks before you should be thinking about running the engine or charging through some means or another. In fairness, I do have a dash cam "on guard" and a tracker, neither of which should be pulling much power, but quite what else is running I wouldn't be too sure.
By way of an example, I had an 85-mile journey yesterday and upon arriving home and letting the battery settle for something like 6 hours, my tracker was showing 12.78 volts and then this morning at 6 it is showing 12.71. So overnight a 0.07 volt drop which might not sound much but in reality translates to something like a 5% state of charge drop. However, in practice I can't use those figures to accurately define volt drop given the relatively warm weather yesterday and the current 3.7 degree temperature!
After a 2-week holiday and assuming the battery was fully charged you should be able to confidently start the motor without any problems, although I would still suggest after 4 weeks you should consider hooking up a battery maintainer just to be sure.