The ECM/PCM whatever you choose to call it, can vary the alternator field winding current to control the target voltage depending on the electrical load, battery temperature, etc.I do not know this for a fact, but I suspect Subaru utilizes a dual mode charging system.
The '21's come with an enhanced flooded cell battery. There is no AGM battery from the factory. If it had an AGM, it would not crap out so soon. I suspect it is the same for '19 and '20. Not sure where it says an AGM is "Required" because they don't come with them installed. "Recommended" Most certainly.These newer Foresters and some other models require an AGM battery.
Although the factory battery on my 2018 is still performing well at 73k miles, I recently picked up an Interstate group size 35 AGM battery when I saw it back in stock at Costco. I live in the hot desert Southwest which is tough on flooded batteries and I suspect my factory battery will crap out before it reaches 4 years old. I've been maintaining it distilled water top offs annually and putting it on a battery tender every 6 months or so.After needing several jumps (fortunately, all in my driveway) I replaced it with the Interstate MTX-35 AGM.
Thank you for that explanation. That helps my understanding a bunch. The battery in my '21 is the Q85 enhanced flooded cell variety, not an AGM. So knowing all that, along with the OP's experience, its obvious now the battery in this new Forester is not a "set & forget" kinda thing. It will need periodic monitoring, especially in light of all the fancy electronics Subaru installed on the car.The ECM/PCM whatever you choose to call it, can vary the alternator field winding current to control the target voltage depending on the electrical load, battery temperature, etc.
You most likely just have a bum battery. Save yourself more aggravation and just go buy a brand name battery and be done with it.My 2021 Forester battery was dead two mornings in a row this week when I tried to leave for work. My VIN begins with a “J” which I am told means that it was manufactured in Japan. I bought the car new exactly 6 months ago and only have 11,000 miles on it. I’ve been made aware of battery drain lawsuits on older models but is it an issue for anyone with a 2021 model? I’ve also been told that only the models made in America are problematic and the Japanese ones don’t have the same battery issue. Is that true? I never leave the back hatch open. I only drive back and forth to work or run errands with it. Suggestions?
I'm thinking about adding the auto stop eliminator however, like @zcrow, I installed a connector plug to my battery so that I can, at anytime plug in my CTEK Smart charger to keep my battery topped off.Exactly what I did for my 2021. Added an auto stop eliminator, added a CTEK battery conditioner with the plug coming through the grill (needed to purchase the extension cable for this). Just keep it plugged in all the time when not in use. I often leave the unused for 2 or 3 weeks at a time and have had zero issues.