Battery Draining Every Two Weeks

[bcrdukes]

Hi Boxster Friends,

I've got a 2001 Boxster S with 139,000KM on the clock (approximately 86,370 miles.) This is my second year of ownership of the Boxster and naturally, second winter with it. Below are some general details for consideration:

Location: Toronto, ON (Canada)
Storage Location: Underground condo parking (not heated)
Battery Make/Model: Interstate MTP-94R H7 (replaced August 2019)
Connected to Trickle Charger: No - Unable to due to lack of electrical outlets and I believe local by-laws do not allow for electrical outlets to be installed in the underground parking lot
Battery history: Replaced with a brand new Interstate battery (I forget exactly the model number, but equivalent factory size) in August of 2019. The previous battery no longer held a charge and was aftermarket.
Alternator: Checked and validated by three shops - No issues with charging system.

Symptoms/Issue: I don't drive my Boxster a whole lot throughout the winter but will attempt to take it out every two weeks to keep her running and to ensure everything is okay.

I know that the car will go into a "sleep" mode after sitting for 5 - 7 days to conserve the battery, but every two weeks, I'll be able to wake it up, try to start the car, but not enough battery to actually start the car; I'd have to jump start it almost every time. I would be lucky to be able to open up the front trunk with what's left. It's been pretty cold lately in the winter, about -5C to +5C / 25F to 41F. I would like to believe that the weather isn't killing the battery here.

I haven't begun diagnosing the issue yet, but any leads or recommendations to check what's draining the battery? I did find a few threads about using a voltmeter to measure the voltage of the battery, and removing fuses one by one to determine if there is a drop in voltage, and narrow down from there. There was also another thread (which I cannot find for the life of me) about some connection point in the engine bay where the starter and/or alternator connect, and possibly being a culprit. Any leads appreciated. Thanks!