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I have read several threads in the forum concerning the battery & would direct you to a thread called "Draining the Battery" While quite long in content, it states an opinion that the OEM battery is not suited for handling any accessory drain with the engine not running. In it gives several suggestions for upgrading the battery to one that is better suited to handle these loads. Or you can choose to continue to put up with the OEM letting you down & have the dealer replace it with another that won't prevent you from having the same situation repeated. I would suggest that you bite the bullet, but the better battery & then file a complaint with Subaru of America & ask then to reimburse you. That's what I have done essentially. Good luck!
I will probably change it out in year three, unless it dies prematurely. I just will not count on it for anything but simply starting the vehicle.
 

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^^ basically where I’m at. If I do sit with the radio on for a short time I ensure the hvac is off (I do that in any car when the engine isn’t running). I also check the battery voltage on the head unit and don’t let it drop too much. Lately it’s been dropping rather quickly so I’m sure I’m due for a battery soon.
 

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^^ basically where I’m at. If I do sit with the radio on for a short time I ensure the hvac is off (I do that in any car when the engine isn’t running). I also check the battery voltage on the head unit and don’t let it drop too much. Lately it’s been dropping rather quickly so I’m sure I’m due for a battery soon.
How can you check the battery voltage on the head unit?
 

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This is an intermittent problem for me. The battery drained once, and I was not sure whether it was leaving the tailgate open, or something the kids did. Sat night I left the tailgate open on purpose, after packing for a day trip, to see what would happen. I have a portable jumper and I knew I would be driving yesterday morning, so it would not be inconvenient. Yesterday morning, the battery was fine.

So, I left the tailgate open again last night (tired and not finished unpacking after the day trip), and this morning, the battery had drained. Starting the car was a very minor task, but then I did have to drive it around for 30 min to make sure the battery was properly charged.

There is definitely something wrong, and as others have noted, it involves having the entire electrical system activated when it should not be.
 

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this might help
Please no. Anyone having problems with a 2019 or early 2020 Ascent hatch killing the battery, please just get your liftgate controller replaced. The new one properly institutes a 20 minute timeout and stops drawing current at the 20 minute mark.

Sorry, I've just seen too many people complaining about having to use hacks to fix this, when there's been a fix for a long time now.
 

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If yours isn't covered under warranty, it's an easy swap and not too expensive of a part. Alternatively, you should look for the "Hatch Catch" for the Subaru Ascent, which is a MUCH simpler hack.
 

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No, not very helpful. Many 2020's don't have this problem, and no 2021's do.

This part adds a 20 minute timeout to the liftgate controller. It's about $133 from most dealerships.


It's covered under warranty for those in warranty, if they fit the criteria of the TSB

That TSB is old and not updated, so, the part number is wrong. The part number is the one I shared in the first link.
 

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No, in 20 minutes, there's no more battery drain.
 

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I'll second that the updated control unit referenced above addressed the drain on my 2019 when the tailgate was left open for extended periods. Thanks to the awesome folks on this forum, while under warranty I was able to discuss TSB 07-143-18R with the dealer for repair. You likely have also experienced other 'erratic behavior' with the tailgate if you're impacted. You'll want to be sure to start with that concern first if you're bringing up the TSB for warranty work. (don't start the discussion with the service writer "hey so I read that the tailgate drains the battery, can you replace this part for free" lol)

Also,
"New PRG control modules (referenced above) were incorporated into production as follows:
• Forester: Starting with VIN LH477261
• Ascent: Start of 2020MY production."

If you're vehicle is newer than those dates/VINs you may have a different issue worth a new thread to help diagnose.

fwiw
 

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Also,
"New PRG control modules (referenced above) were incorporated into production as follows:
• Forester: Starting with VIN LH477261
• Ascent: Start of 2020MY production."
This is no longer correct, and applies to the older controller mentioned in the TSB. So, if any of you have a 2020 that still drains the battery after 20 minutes of the gate being open, you may need the newest design liftgate controller.

Sorry, my bad... I should have spent more time clarifying that, especially since I didn't have the newest version of the TSB available.
 

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I own 2021 Ascent it just happened to mine so issue os not fixed. Had no cell reception so it was very difficult to get help. Really disappointed with Subaru as this is my 9th Subarus and this could be last.
 

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I own 2021 Ascent it just happened to mine so issue os not fixed. Had no cell reception so it was very difficult to get help. Really disappointed with Subaru as this is my 9th Subarus and this could be last.
What happened to yours? The timeout works on the 2021 Ascent. But, the timeout resets every time you open any door, or re-open the liftgate. What were your particular symptoms?
 

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What happened to yours? The timeout works on the 2021 Ascent. But, the timeout resets every time you open any door, or re-open the liftgate. What were your particular symptoms?
I have no idea but we did leave liftgate and some other doors open for quite a while not knowing this will drain the battery. I have camped with 2017 Outback(with power liftgate) and 2019Crosstrek which I previously owned with no issue so I wasn’t expecting this from our newer Ascent.
 
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