Car parked in garage, how long will battery.....

If you turn off the Smart Key System (SKS; button under the steering wheel that says "Key"), you should have no problem leaving it for 2 weeks at a time (or longer, probably). In reality, you could probably leave the SKS on, but that's the primary battery drain, so turning it off means even fewer battery troubles. With the SKS off, every two weeks should *easily* be often enough; you could probably even stretch it to once a month, if you needed to.

Of course, with the SKS off, whoever drives it for you will have to push the button on the remote to unlock it and have to physically insert the key into the slot in the dash.

 

It is likely that the 12V auxiliary battery will discharge after 2 months. You can either have your friend make the car READY for 30 minutes every two weeks (not necessary to actually drive the car) or else disconnect the 12V battery before you leave on your trip.

One way to disconnect the battery is to open the hood and find the main relay/fuse box near the inverter. Open the lid by pressing hard on the latch at the front of the lid. Find the dedicated jumpstart terminal covered by the red cover, lift up the cover, then remove the nut that is revealed (need 10 mm socket and socket wrench).

Lift off the wire terminal that the nut had secured. Replace the nut. Lower the red cover. Put the wire terminal on top of the red cover. Now the vehicle should be totally powered down.

Replace the relay box lid and lower the hood. Lock the doors manually, and the car is ready for storage.

 

In 2006 I deployed to Guam for 4 months. During that time I left my battery negative cable disconnected. When I returned, the 12V battery still had a full charge, and the traction battery was unchanged at a full compliment of the blue bars. I even got 49 MPG on that tank.

I like Mr. Wong's method of disconnecting the underhood connection. Popping the rear hatch with no power is a slight challenge.