My time of owning the Forester is too short to comment on it specifically, but I've never owned a vehicle yet that couldn't sit (excluding serious cold) for a couple of months and fire right up without a problem unless there was something wrong with the battery or electrical system.

 

It really is dependent on how many things are pulling a draw on the battery (with the key off) AND the configuration of the battery. Not all batteries are equal and certain newer gel type and other deep cell batteries will provide much longer time on a charge.
You can buy a larger battery or buy one of these "battery tender" devices which will keep them batteries "hot" all the time. Some are the type you plug into the electrical wall outlet and others are solar powered.
You might look into one of these.
I use Solar Panel Recharger on my lawnmower. :biggrin:

 

I just returned from a 3-1/2 week vacation and my 2011 Limited fired up instantly.

 

There are several things that will cause parasitic drain. I'm not familiar with the power requirements of the MOGO gps trakcer so I can't comment on that.

I rarely drive my car and after a couple years of driving it every so often I could only go a few weeks before I would notice some trouble starting. That was with a Optima Yellow top battery.

It got so bad that I eventually replaced the battery with an average car battery. I have been trying to drive it more and charge it over night but even after a couple weeks it sounds less willing to start.

If his battery was new, and fully charged, its surprising that after 2 weeks it would be dead unless the GPS tacker sucks up a sizable amount of juice.