I believe your 2020 came with an Enhanced Flooded Battery (EFB). Just make sure the after-market replacement is an EFB including correct size and CCA's.
Considering all the complaints on this forum re Subaru batteries I would take my chance with the unknown brand after-market, assuming it is an EFB.

 

I miss the days when a car-battery was about $40 for the largest battery which would fit.
...of course, a NEW car was under $8K too

 

@BruceP

Kinda relevant but, I've been trying to find the cheapest battery for my other non-Subaru vehicle since it needs one. I found Tractor Supply sells a battery for $70 in my area.

 

Your 2020 Forester Limited will easily accept a Group 35 battery. Assuming that the aftermarket battery that you are being quoted is a flooded cell or enhanced flood cell battery, it's pretty pricey. Around here, you can get a decent AGM Group 35 for about the same price. That would be plus installation, depending on where you buy it.

An enhanced flooded cell battery is said to hold up to the multiple cycles of automatic-stop-start better than the basic flooded cell. Because of the heat here, I would not use either. Climate may be different where you are.

I installed an Interstate AGM in my 2017 Outback in 2019, and it was going strong when I sold the car in 2024.

 

Your vehicle came with a Q85 EFB battery from the factory. It was around the size of a Group 35 battery, but was a bit low in capacity to really work well with the AS/S system. The "Settlement" provided a larger battery (about the size of a 24F) with substantially higher CCA and RC, along with a new plastic retainer plate (edit: "tray"). There is adequate room for the longer battery, and the wiring harness has enough slack for you to go this route too.

Subaru new replacement (SOA821B900 believed to be made by Exide / Stryten) provides around 750 CCA, 120 RC, 76 Ah and measures like a Group 24 (slightly short). BTW, if you want to go aftermarket, the Duralast Platinum 24F-EFB is practically identical.

 

I put in the size 24 when my battery was being replaced. It is a larger battery and you need to get a different battery tray. I did this when mine needed replacing and got an EFB from Autozone. The AGM batteries charge differently than conventional or AGM and may not last as long unless the "smart" alternator knows how to charge the battery. Many threads on this in other forums

 

REMINDER:
Many autoparts stores will INSTALL FOR FREE with battery-purchase.
BEWARE: Not all of their employees are mechanics 😏

 

AGM batteries are supposed to be charged before first use.

Your charger needs to be able to charge AGM batteries. Using a charger for traditional batteries has the potential to destroy it.

Harbor Freight sells a charger for $69.

 

AGM batteries are supposed to be charged before first use.

ALL automotive batteries should be charged before first use.

Lets not forget that both Flooded and Absorbed-Glass-Mat batteries use the very same electrolyte. (sulfuric acid)

Infact, these two types of batteries are more similar than they are different. They are all Lead-Acid.

The flooded cell batteries are usually shipped DRY (no acid within them) and the acid is added before putting into use.

Many flooded batteries I buy (motorcycle...etc) come with a container of acid which the USER must add to the battery before use. The instructions CLEARLY say to fully-charge before installing into vehicle.

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Technically: All Lead-acid batteries start to 'age out' once the acid is installed. By shipping them dry, the battery truly is BRAND NEW when acid is added and it is charged.

This is one reason I purchase my batteries at "Interstate Battery" store. They add the acid and charge the batteries onsite before purchase. They sell so many batteries that you can be sure it has had acid in it less than a week.

In other words, buying a battery which has been sitting on the shelf with acid in it for months or years ALREADY has some 'age' on it which subtracts from the lifespan you can expect out of it.

 

And while we're at it, I probably should mention TSB regarding the rather delicate battery sensor. This shunt assembly is part of the alternator charging feedback loop. Treat it with care and follow the removal procedure and torque recommendations. It's a $100 part that you don't want to break. Ignore the 2019/2020 dates. Applies to all SK years.

 

Thank you, @Fibber2! This is useful and I've stuck it into my library. The procedure makes common sense because the connection just looks right when done right. But how many people know what looks right, if the bolt goes on?

 

I went with the Interstate AGM MTX-35 in my 2019 Forester and 2021 Crosstrek (2.5L). I also turned off the silly A-S-S on both cars

 

I lime the AGMs for several good reasons.
As for A.S.S., I wonder when that will disappear once hybrids become the more sane standard that eliminates the need to repeatedly stop and start the engine.

 

To be on track, there is nothing special about Subaru OEM batteries that justify the premium price.
AGM batteries that Subaru doesn't offer have some advantages, in no internal maintenance and lack of corrosion.

At the risk of going further off track, yes I know, and Subaru has one of the lower capacity motor power batteries apparently, but for stop and go city traffic, it's preferable to ICE only A.S.S. as the hybrid uses the Atkinson/Miller-cycle engine.
The longer warranty on the hybrid components is a good thing.
The not so good thing seems to be that the battery is limited to being air cooled and is really small at .57kwh..

 

I have 2 2020 sports and replaced both batteries with the everstart agm battery from Walmart for 179.84. They have a 4 year replacement warranty. No problems with them