Toyota GR86, 86, FR-S and Subaru BRZ Forum & Owners Community - FT86CLUB

So after 3 batteries, 3 different chargers, and 2 visits to the dealership - the Subaru Western US Field Technician (cool title huh?) spent two days taking a look at what was going on with my BRZ battery system.

Essentially there are 2 culprits that will have a negative impact on your battery if your car is sitting around.

The first is if you have a keyless start fob and it's within radio range of the car, the car will never enter sleep mode. This will cause the car to consume up to 10x the power compared to if it enters sleep mode. The range spec on that is 15 feet however, my driveway is maybe 20 feet from where I hang up my keys to where the car is parked (and there's a wall). Do they make faraday cages for key fobs? I guess the other solution is to buy a bigger house where the garage is further away... :bonk:

OK so the simple answer is to wrap your fob in tin foil if you're planning on not driving for a while; I sound like a government conspiracy theorist now.

The second is the evaporative leak control module which will cycle on and off even if the car is turned off.

The field tech was able to confirm the behavior of my car is consistent with the TSB # 07-85-14

Bulletin Description: This bulletin will provide the proper procedure for measuring Dark Current (parasitic battery draw) along with the specification for maximum allowable limits. Customer concerns of batteries going dead over a period of time should be diagnosed using this procedure once any obvious contributing factors have been eliminated.

Basically this behavior is normal and I need to find a way to keep my key fob and car further apart so it can properly enter sleep mode.

Something to noodle on if you're noticing a weak battery after only a week or so of no driving.