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Discussion Starter · #1 ·
Last night I got in about 12m and took some things out of the back. I forgot to close the rear hatch (my fault!) and this morning about 8am I tried to start the car, but the battery was dead (just got clicking). It started right up with a jump, but my experience leaves me with several questions/observations as keeping the interior lights on for 8 hours should not drain the battery:

1. Is the reserve capacity of the OEM battery too small for the car.
2. Is the drain too large on the battery so that an 8 hour bulb burn drops voltage below needed to start
3. Why does the car (with its touted "smart" technology) not smart enough to shut down when the battery drain reaches a critical level
4. Why does the light not time out.

I realize it was my fault, but with all the tech in the car I would think that keeping the battery alive is a minor fix. There is much more chance of me draining the battery then some complex programming like not keeping my eyes on the road, etc.

Also, the car was parked in an unheated garage with the temp about 40f when I tried to start it. The car has been in service about 2 months
 

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2015 2.5i Premium
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1,308 Posts
1. Is the reserve capacity of the OEM battery too small for the car.
Nope

2. Is the drain too large on the battery so that an 8 hour bulb burn drops voltage below needed to start
Pretty much yes. There are multiple lights on in the interior when the doors/hatch are open. Incandescent bulbs like suck power.

4. Why does the light not time out.
Not sure on this one. I think the only main dome light times out on my 15, but not 100% sure.
 

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Super Moderator
2001 Forester S, 4EAT
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2,864 Posts
If it is a group 35 battery that is a approx., 44 Amp-hour. But that is to 0 Volt, so using 1 Amp-Hr drain rate and only draining to say 50%, you're still looking at about 20 Amp-Hour Left. Also without knowing exactly how fully charged the battery was when you left the hatch open, say you had may 80% charge left, means you started at approx., 35.2 Amp-Hour, giving you about 17 Amp-Hr at 50% overnight discharge. I can tell you that 17 Amp-Hr is about the power my motorcycle battery has. So I seriously doubt there was enough power left to start the next morning.

You did not buy a Mercedes Benz, Audi, etc...one of the other Luxury brands where the electrical circuit does exactly what you ask, which is shutdown after sensing a certain voltage level from accessories being left on/plugged in. I own both a 2001 Subaru Forester and a 2014 Mercedes ML 350. What you call "smart" technology is primarily found on Luxury vehicles like the Mercedes. Even my 2013 Nissan Leaf SL (Top Model) does not have this shut down feature.....
 

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2017 Forester 2.5i
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28 Posts
What you call "smart" technology is primarily found on Luxury vehicles like the Mercedes. Even my 2013 Nissan Leaf SL (Top Model) does not have this shut down feature.....
My 2013 Fiat, did, however.

It's not magic, nor is it expensive. I just don't think it's a priority for Subaru.
 

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1999 A/T - 235,000 mi. WA state
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889 Posts
... keeping the interior lights on for 8 hours should not drain the battery:
Well, think that is normal experience for a lot of cars;
it's what I was told to avoid doing for just that reason.
 

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2012 Forester X 5 MT
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881 Posts
When it becomes time to replace your battery, consider a 24F size. It has the same width/height but is an inch or so longer. It will fit with a simple slice in the back of the foam battery "cozy" - if your battery has one.

You get lots more Amp-Hours for the same price.
 

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2019 Touring CVT
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305 Posts
I found this in the Forester 2019 manual. Apparently not doing it’s job.

Battery drainage prevention function
S02AC03 If a door or the rear gate is not completely
closed, the interior lights will remain illuminated as a result. However, several lights are automatically turned off by the battery drainage prevention function to prevent the battery from discharging. The following interior lights are affected by this function.
Item
Map lights
Dome light
Ignition switch light
Cargo area light
Automatically turning off
Approximately 20 minutes later
Approximately 20 minutes later
Approximately 20 minutes later
Approximately 20 minutes later
2-6. Alarm system

Switch position
DOOR
DOOR

DOOR
S02AF
NOTE
. The default setting for this function is set as “operational”. The operational/ non-operational setting of this function can be changed by a SUBARU dealer. Contact your SUBARU dealer to change the setting.
. When leaving the vehicle, please make sure that all doors and the rear gate are completely closed.
. The battery drainage prevention function does not operate while the key is in the ignition switch.
 

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Premium Member
2017 Forester XT CVT (High Torque)
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254 Posts
If you want to add automatic battery protection, you can install a PriorityStart battery minder. I did in my ‘17 XT.

Since this model year has a big power distribution module attached to the positive terminal (under the big red cap), I couldn’t relocate it very far without some fabrication. So I managed to just squeeze the PriorityStart heavy duty in between the battery and engine. The unit is zip-tied to the battery tie-down and the foam surround.

Before:


After:


The location is close to the engine block and coolant pipes, but it’s pretty solid and I don’t think it will melt. The red cable attaches the PriorityStart to the battery, the positive terminal from the car is attached to the beefy stud on top of the unit. The PriorityStart also attaches to the negative battery stud so it can power itself. The black wire also can be installed with a momentary switch inline to force the battery to be connected/disconnected manually.

In normal operation, the unit mechanically cuts off the battery if the voltage across the circuit dips to 11.7v. There is logic to prevent the battery from being disconnected if the engine is running. You can hear the mechanical whir of the gears when it disconnects, even in the cabin. A foot on the brake pedal should reconnect it, but my LED taillights don’t draw enough current, so I also have to turn the key.

I also installed an Optima Yellow Top battery, which is a safe gel battery that can be deep cycled. It works great and has more total power and lasts longer than a regular battery. I can feel the difference when I crank the starter, but it takes longer to charge fully than a regular battery with just the OEM alternator.
 

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2014 Subaru Forester CVT
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2 Posts
The OEM unit is weak, particularly for those who live up north. I have two teenage daughters and they don't pay a whole lot of attention to things. Twice they've left the dome light on overnight, both times it killed the battery. Car was unable to turn over in the morning. I recharged, but finally replaced the battery this year with an EverStart MAXX-35N from Walmart (640CCA, 5-year warranty). I did get four years out of the OEM, but probably should have replaced after three. Bottom line is it takes a lot of juice to get my '14 started if its more than 10 degrees below zero (F) and three years is probably about as long as you should reasonably expect out of the OEM under those kind of conditions.
 

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Sahuarita, AZ 2018 Forester Limited
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2,812 Posts
According to my owners manual, the 2018 Forester also has the Battery Drainage Prevention function (except for the door step lights).
 

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2019 Forester Touring CVT
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67 Posts
The OP has a 2019, the Auto Start/Stop system may come into play here.

Someone posted a link to a govt funded study on the pro/cons of the Auto Start/Stop, the one piece I took away from the article: "It takes 6 miles of driving to replenish the battery after an engine start" (sic). Based on this I try to disengage that system when getting close to home.

Prollly not an issue with a new battery but why not keep it topped off if possible.
 

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18' 2.5 Premium 6MT
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180 Posts
48Ah is pretty weak, a quick google has revealed batteries of at least 65Ah are available. For a utilitarian-ish vehicle I think it would have been great for Subaru to include a voltage meter, the MFD could easily display one with a software update. Using the Torque app you can see this information to get an indication of whether your voltage is less than the 13.8V it should be for a healthy unit.
 

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2019 Forester Touring CVT
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222 Posts
Even my 2013 Nissan Leaf SL (Top Model) does not have this shut down feature.....[/QUOTE]

My 2011 Altima Coupe has the shutoff feature!

Wonder if you can convert to LED inside lights?
 

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2019 Touring
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242 Posts
Anyone know what the Parasitic Battery Drain is on a 2019 Forester? I'm planning to be away for several weeks and am considering a battery conditioner like the ones I keep on my motorcycles.
 

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2019 Touring CVT
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305 Posts
I don’t know about the 19, but I leave my 15 Tourings for up to 3 weeks at a time and they start up easily.
 

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1999 Forester S
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530 Posts
Anyone know what the Parasitic Battery Drain is on a 2019 Forester? I'm planning to be away for several weeks and am considering a battery conditioner like the ones I keep on my motorcycles.
Just drive it around on the highway for 20 minutes or so, that'll ensure you park it with as full a charge as you can get.

It should still start after several weeks of inactivity, but if you're really worried about it, just disconnect the negative terminal...
 

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18' 2.5 Premium 6MT
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180 Posts
If you want to add automatic battery protection, you can install a PriorityStart battery minder. I did in my ‘17 XT.

Since this model year has a big power distribution module attached to the positive terminal (under the big red cap), I couldn’t relocate it very far without some fabrication. So I managed to just squeeze the PriorityStart heavy duty in between the battery and engine. The unit is zip-tied to the battery tie-down and the foam surround.


Before:


After:


The location is close to the engine block and coolant pipes, but it’s pretty solid and I don’t think it will melt. The red cable attaches the PriorityStart to the battery, the positive terminal from the car is attached to the beefy stud on top of the unit. The PriorityStart also attaches to the negative battery stud so it can power itself. The black wire also can be installed with a momentary switch inline to force the battery to be connected/disconnected manually.

In normal operation, the unit mechanically cuts off the battery if the voltage across the circuit dips to 11.7v. There is logic to prevent the battery from being disconnected if the engine is running. You can hear the mechanical whir of the gears when it disconnects, even in the cabin. A foot on the brake pedal should reconnect it, but my LED taillights don’t draw enough current, so I also have to turn the key.

I also installed an Optima Yellow Top battery, which is a safe gel battery that can be deep cycled. It works great and has more total power and lasts longer than a regular battery. I can feel the difference when I crank the starter, but it takes longer to charge fully than a regular battery with just the OEM alternator.
Interesting, i just looked at my 18' and it has a 63Ah battery, your 17 has a 43 and it sounds like the 19 does as well? Did i get a fluke or did Subaru change by model year?
 

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