I know this wasn't intentional, but when I click this link, I get a "No such item" error message, which I find to be ironic given the nature of this discussion. The link just has a trailing semicolon that needs to be removed, though.
I have a 2016 Subaru Forester with a seemingly parasitic drain issue. Every time I go to start the car, it's like rolling the dice whether it has enough battery power to fully start. I have a portable jump starter that I've had to use at least 20 times or so in the last couple of years. This has been happening even well before the 3G sunset period, so that is not the only source of the battery drain problem, for which there is a class action lawsuit: https://www.subarubatterysettlement.com/.
Everything I've read online about the issue points to the STARLINK system, and the common wisdom in this thread and elsewhere is to pull the DCM fuse. Unfortunately, my Forester has no such fuse, so I'm at a loss what to do with my car.
It's so frustrating, because my wife has a Subaru Crosstrek of the same year that has never had a battery problem, even with the OEM battery. She has a base model without any additional "upgraded" electronics, so that's the likely culprit in my case. I'm currently on my third or fourth higher CCA battery and had to jump it again a few days ago.
I haven't taken my car to the dealer for the parasitic drain issue, but previously tried to get dealership service for an unrelated entertainment system issue related to USB media playback freezing up the entertainment system. That fix was unsuccessful, and I have no faith in Subaru mechanics being able to diagnose and fix a potentially more nebulous battery drain issue. It doesn't help that the dealership is now 45 minutes away, so I'm not interested in wasting even more time on a hit and miss solution.
Ironically, I bought Subaru because reliability was my number one concern when purchasing a vehicle, and I'm not sure I would do that again.
I just went through something similar with my vehicle, had a relatively new expensive AGM battery about halfway through its 3 year warranty. Would not start if left for 4-5 days which slowly crept down to 2 days.
Seemed like a parasitic draw but pulling fuses and using a multimeter verified idle draw at 30 milliamps which is within spec. If you find high like a few hundred milliamps you can start pulling fuses to narrow down offending item.
In the end it was a bad a battery, but was difficult to get the warranty replacement because it could be charged and work again so long as you ran it every day.
It's relatively easy to verify parasitic draw and make sure it's in that 30 milliamp range, with even a cheap multimeter by disconnecting negative and running through multimeter. Tricky part with modern cars is getting it to go fully to sleep, anything can trigger wake up (like opening the door) and it can take a few minutes for it to fully sleep to idle draw.
I learned over the pandemic that a Toyota Camry Hybrid would eat its 12V AGM battery very easily. In this case, it is a deep-cycle AGM and isn't even used to start the ICE. It's "just" to run accessories and boot up the power control system that engages the much larger hybrid battery.
One such Camry in our extended family was parked for a few months and the battery failed. We got an expensive OEM replacement and tried to make sure we drove the car every week or two. It failed again in just under three years. Meanwhile, we have an entry-level Audi that also often gets only a short local trip every week or two. It is still on its original AGM battery after 6 years, and this one has to actually start the ICE.
So, I am disappointed to find that Toyota engineers could not be bothered to apply whatever basic power management logic the Audi folks did to protect the battery. Worse, the Camry has this big NiMH traction battery, and I would have imagined some clever backup strategy to infrequently top-up the 12V battery if parked too long, so it would be reliable.
In the end, I gave up and installed an old-school battery cut-out switch, so we can just disconnect the 12V battery if not planning to use the Camry for more than a few days. Every time I operate it, I'm giving the Toyota engineers a rude hand gesture in my mind.
Smart electric drives prior to 2016 used their “[not] clever backup strategy” to cyclically try to keep a failing 12V battery charged and that could result in flattening the traction battery and eventually bricking it.
Ha, that does sound somewhat un-smart. Of course, when I imagined clever, it would include enough state and timer-based behaviors to recognize a bad trend and protect the traction battery too.
It should be feasible to monitor voltage levels and rates of change and signal an error condition rather than silently destroy itself...
There is an ECU flash at the dealership that supposedly fixes the parasitic battery drain. I've replaced my battery a couple of times, but haven't had an issue since the ECU flash.
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