Before spending hours or money replacing parts I would eliminate basics and get the battery checked even though it's new, check the alternator is actually charging looking for 13v -14.5v at idle. Examine the integrity of main earth and connections and then eliminate common silly drains like internal or boot (trunk) lights staying on.
Then it's time to get busy with a meter to find the parasitic drain by taking readings over the circuit to see if there is an abnormally high reading, only problem is establishing the normal baseline since most cars will draw quite a lot for up to 15-20 mins after shut down to maintain some fans, modules etc. I don't have the specs for the Zed but might expect to see little more than 100-200ma once fully shut down (note that open doors or otherwise 'waking up' the car will initiate some components to draw current again). If a reading is in the 500ma -1amp+ range that could quickly run a battery down. Really tricky faults can be caused by things like faulty central locking/alarm modules cycling on/off at the end of the run down period mentioned above, I've discovered these in the past by hanging around for a bit after locking the car a listening for tell-tale whirs or clicks.
Once you establish an abnormal draw remove fuses to isolate the offending circuit when the current drops to normal. Then it's a matter of replacing the fuse and methodically disconnecting items on the circuit or taking readings over components. Items like alternators, starter motors or modules will often feel warm which gives the game away as well.
I know that's not really the answer to your post, the original audio head units are common cause on BMWs, and another forum member recently had similar problems caused by a cold start pump, but many components can also cause this and it can be quicker to go through a basic meter test.
Good luck and let us know if you crack it.
