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2018 Outback 2.5i Limited, No Eyesight, No Navigation
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Discussion Starter #1
(Although there are many battery threads, I did a search and could not find one dedicated specifically to this topic.)

I would like this thread to be dedicated to ways people are battling the dark current drain. I am not interested in “take it to the dealer” suggestions. The point here is to prevent battery drain problems in the first place. Reading the manual, I stumbled across some things that are worthy of more highlighting.

Here are some things I am doing or am planning on doing:

1. Disable fob communication while in my house or when he fob is near the car. The manual describes how to do this on the fob. It takes about 2 seconds. Another way is to wrap in foil or the like, but making a faraday cage is less convenient when away from home or whatever. I figure without communication, the car will go into a lower power state. Who knows? Anyway, it is worth the small effort.

2. Disable the car’s fob sensors if the car sits for awhile. It should be a relatively big dark current drain to keep the sensors constantly looking for the fob. I highly doubt most OB owners are remotely thinking about disabling the sensors. The steps to disable the sensors are quick once you get them down. BE CAREFUL BECAUSE IT IS POSSIBLE TO LOCK THE FOB INSIDE CAR. Make sure you know your rear gate PIN.

3. Get an AC-powered battery charger/maintainer for home garage. These devices are discussed extensively in other threads. Please share links, model numbers, and reviews.

4. Get a solar-powered maintainer when OB is parked at the airport or in sun for several days. Please share links, model numbers, and reviews.

5. Get a better battery. This is also discussed extensively in other threads.
 

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2016 Outback 3.6R Ltd. w. Eyesight
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Good idea. I haven't had a problem yet with my 2016, but I keep a lithium jump pack on board just in case.

Please let us know how to do #1 and #2 and the pros v. cons of doing so.

#3. Never used one for a car, but I've used Battery Tender brand "smart chargers" for my motorcycles for many years. They're expertly engineered float chargers and I've never had one fail.
 

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2016 Outback Premium 2.5 CVT w/EyeSight+SRVD
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Before concluding that "dark current" is a problem, you should actually measure it on your own vehicle. There's no substitute for your own data.

Measured dark current on my 2015 Legacy Premium is ~30 mA, well below Subaru's published spec of 70 mA maximum, and I've never experienced a no-start in it. Even at 70 mA, a fully charged OE battery should last more than three weeks before discharging below 12 volts (25% state of charge). YMMV.
 

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2018 Outback 2.5i Limited, No Eyesight, No Navigation
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Discussion Starter #4
Attached are pages 2-18 through 2-21 of the Outback 2018 manual.

Actually, it is so easy to disable the fob and disable the sensors, I am going to do my steps 1 and 2 every time I come home as practice.

By the way, I forgot about the lithium battery jump start method, which is definitely relevant here.
 

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Lawn ornament XT
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Somebody needs to hitch up an ammeter with a logger or pen register. It sounds like the dark current is variable and it would be pretty cool to know what the real rules are.

Does it waste power pinging the LTE connection for starlink telematics etc? Does this use more power when reception is marginal, like most other mobile telecom devices?

Does it waste power listening for the key fobs? Does that change if the fobs are further away?

How much power is used for the PZEV evaporative purge? Same amount every night?
 

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2017 2.5i Premium Outback w/Eyesight, Venetian Red Pearl
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So is the dark current drain mostly with vehicles with key fobs? I don't have that feature but have noticed the stock battery drains off after just sitting for some amount of time.
 

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2018 Outback 2.5i Limited, No Eyesight, No Navigation
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Discussion Starter #7
Before concluding that "dark current" is a problem, you should actually measure it on your own vehicle. There's no substitute for your own data.

Measured dark current on my 2015 Legacy Premium is ~30 mA, well below Subaru's published spec of 70 mA maximum, and I've never experienced a no-start in it. Even at 70 mA, a fully charged OE battery should last more than three weeks before discharging below 12 volts (25% state of charge). YMMV.
To me, any dark current drain is a problem. I want the dark current drain on a sitting car battery to be 0.1 mA or less. I understand that is unlikely possible, but that is what I want nonetheless.

Anyway, the manual recommends in bold text to disable the keyless access functions if the car is going to sit for awhile (p. 2-19 in my manual). Besides a dark current drain, why would Subaru recommend that?
 

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'03 outback limited, '01 Outback Limited, '01 Legacy L wagon, '96 Legacy Brighton wagon
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Battery switch - solid state switches are available that can cut off ALL power from the battery so that only the battery's normal leakage is still happening:

https://www.waytekwire.com/products/1408/Disconnect-Switches/&Type-Series=Solid-State

Not sure if there are higher-amperage versions than this one: 300 Amp Battery Disconnect Switch| Solid State Battery | Data Panel You could always wire a couple in in parallel. Activate by a switch in the console.

No idea, though, if you could run a bypass wire to the CPU to keep it from being powered down. I would expect, of course, that you will lose all other custom settings on everything else in the car.
 

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2015 3.6R Limited w/ES
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Since I've never had serious battery problems, I'm not likely to be investigating the effect of disabling the prox key, but my suspicion is that this will gain you very little in terms of reducing dark current. BTW, from what I've read (and IME), the fob has to be very close (maybe a couple feet) to the vehicle for the proximity system to detect it. You have nothing to worry about if you're more than a few feet away, much less in your house.

As for a charger/tender, the CTEK 7002 is widely accepted as one of the best. A little on the pricey side, but it can output up to 7 amps (so it's capable of charging much faster than a typical battery tender), performs automatic desulfation, and has a recondition mode for deeply discharged batteries (which I was finally able to try and it worked very well on a 6 year old Die Hard that was showing its age).
 

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2017 2.5i Premium Lapis Blue
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Good idea for a thread. This looks like a good place to add a little anecdotal evidence that might be of interest even if not absolute.
I've pushed back a little on the idea that a better battery isn't much of a solution to dead batteries. As a reference I installed a Group 24 Everstart battery a couple of months ago. Since then I have had no problems with starting the engine even after sitting with the door open and the ignition on and off while setting up my Scangauge a while back. Temperatures here over the last couple of weeks have dropped well below 0F with daytime highs in the single digits.

But, while I haven't had any starting problems with the new battery I have seen reason to monitor the dark current drain issue. I drove my truck for about 5 days during the really cold weather after putting a new battery in that so I could make sure I didn't have any charging problems with it. The Outback sat in the driveway during that time without being started. I had the Scangauge hooked up and before starting the engine after those 5 days it showed a battery voltage of 11.0 volts. The car started with no issue and running voltage was 14.1 volts. I've monitored the voltage while driving and the Scangauge shows from 14.0 to 14.2, never lower and never higher. I also have one of those USB chargers plugged into the "cigarette lighter" and that just about always shows 14.4 volts running. I've never looked at that one without the car running and I'm pretty sure there isn't power there after the key is shut off (yes I have the key and not the push start).

I've been wondering about the accuracy of the voltage through the Scangauge and the USB charger, or if reading the voltage with the key on is an accurate read of battery voltage, but I keep forgetting to stop by my shop to get my multimeter to check it directly to compare. Now, moving on to today, I had my oil changed at the dealer (side note: first oil change I have ever paid somebody else to do in my life). They did their usual multi-point inspection and when he was going through the list of everything he said the battery checked out not just "okay" or "good", but checked out "really good". Probably didn't mean anything but I got a little chuckle out of it anyway wondering if anyone with the stock battery ever got that in their report.

Anyway, back to the topic of this thread. I'm going to get on the other side of the fence and accept that maybe a battery tender might be useful more often than I thought. I'm not going to plug it in on a daily basis, but I am going to hard-wire a cord and run it out through the front grill, probably along with the cord for the block heater I am having installed in a couple of weeks. Then when I am not going to drive the car for a couple of days or more I will plug in the battery tender.
 

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.... Anyway, back to the topic of this thread. I'm going to get on the other side of the fence and accept that maybe a battery tender might be useful more often than I thought. I'm not going to plug it in on a daily basis, but I am going to hard-wire a cord and run it out through the front grill, probably along with the cord for the block heater I am having installed in a couple of weeks. Then when I am not going to drive the car for a couple of days or more I will plug in the battery tender.
It is a good idea to use charger on a car battery a couple times a year. This will equalize the cells within the battery and extend the life many years.

I realize anyone can research "battery equalization" In short - this is a process which brings ALL the cells up to a known state so they are working in unison.

As a battery is used in daily driving, at least one cell is weaker than the others and never fully recharges. Since all 6 of the cells are wired in series, it is not unlike a chain with a weak link. This weak cell dictates the maximum power the ENTIRE battery can produce.

Modern automobile charging-systems are designed for FUEL EFFICIENCY and the alternator is tuned to load the engine as lightly as possible to meet EPA regulations. This makes battery-life suffer. One should NEVER expect the alternator to fully-charge the battery unless you drive for many hours.
 

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2018 Outback 2.5i Limited, No Eyesight, No Navigation
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Discussion Starter #13
Does it waste power pinging the LTE connection for starlink telematics etc? Does this use more power when reception is marginal, like most other mobile telecom devices?
I read about somebody disabling Starlink by removing the fuse.

NO BIG BROTHER!!! How to disable Starlink

Has anybody tried that? Come on, people. Let's go. I can't be the craziest one here!
 

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2016 Outback 3.6R EyeSight, 20mm RSB, STB, 2" ECOhitch
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This is actually not very good information. I have been using solar panels on my boat for over 2 years now. I use a controller to maximise output and have documented their performance. I have 240 watts of panels and the most I have ever seen out of them is 180 watts at peak summer sunshine in Southern California, winter gets max around 100 watts max. You only get max for 2 hours in the middle of the day, before and after it tapers off. Clouds and shadows will reduce or eliminate output. So if you do the math:

A 24 watt panel placed on the dash (but wired to the battery) will loose output due to the windshield blocking the sun (-20%, angle to the sun (-30%). So my best guess is max 12 watts at peak output in Southern latitudes, less if you live up north. All we care about here is Amp Hours. So from your 24 watt solar panel you might realistically expect 6 AH per day, summer in the South. 2-3 AH/day in the winter north. If your car only uses 300ma for parasitic drain that is 7 AH/day. But your drain could be as high as 15 AH/day depending on a variety of conditions. So a 24 watt panel will not charge your battery but will make it last longer, but how much it works depends on where you are, how you park and the weather.

That said: a 24 watt panel might be cheap enough to install and if you need to leave the car for a long period of time, can part in full sun, it will help. Anything smaller would just be a waste of money. IMO

If you have power available then a battery maintainer will make your battery last longer, a good AGM might last 10 years if you can prevent it from being discharged constantly. Even a small 1 amp unit would be enough. I don't use one on my OB but might when I buy a good battery. Otherwise just plan on putting in a cheap battery every 2 or 3 years. Might be worth the hassle.
 

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Discussion Starter #15
A 24 watt panel placed on the dash (but wired to the battery) will loose output due to the windshield blocking the sun (-20%, angle to the sun (-30%). So my best guess is max 12 watts at peak output in Southern latitudes, less if you live up north. All we care about here is Amp Hours. So from your 24 watt solar panel you might realistically expect 6 AH per day, summer in the South. 2-3 AH/day in the winter north. If your car only uses 300ma for parasitic drain that is 7 AH/day. But your drain could be as high as 15 AH/day depending on a variety of conditions. So a 24 watt panel will not charge your battery but will make it last longer, but how much it works depends on where you are, how you park and the weather.

That said: a 24 watt panel might be cheap enough to install and if you need to leave the car for a long period of time, can part in full sun, it will help. Anything smaller would just be a waste of money. IMO
Yikes! I am looking at a car battery solar maintainer on Amazon that is only 7.5 W.

http://a.co/03sTMQZ
 

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This is actually not very good information. I have been using solar panels on my boat for over 2 years now. I use a controller to maximise output and have documented their performance. I have 240 watts of panels and the most I have ever seen out of them is 180 watts at peak summer sunshine in Southern California, winter gets max around 100 watts max. You only get max for 2 hours in the middle of the day, before and after it tapers off. Clouds and shadows will reduce or eliminate output. So if you do the math:
Great post!

I hand-built the solar power system at our beach cottage, and your math is very much in line with the practical results we get out there.

One other factor to consider-

If the car is going to use 7AH per day, you may need to recover more than 7AH from the panels. If the draw occurs only when the panel is providing power, you can get away with only replacing that 7AH.

If the draw can occur at night, then you'll need to store that electricity in the battery until night, and you lose efficiency that way- thus needing even more power from the panels.

Yet another limiting factor with the solar chargers is snow cover. I'm not sure how much, if any, a solar charger would be putting out when the car is covered.
I can tell you with confidence that a lousy quarter inch of snow can cancel more than 90% of the panel's ability.
 

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It is a good idea to use charger on a car battery a couple times a year. This will equalize the cells within the battery and extend the life many years.
Good comment, but I just wanted to clarify something here. The high quality float/maintainer (Battery Tender, NOCO, CTEC, etc.) probably won't do the trick here unless you select a mode (varies by model) to execute this. Equalization typically requires an overcharge state, something float/maintainers are specifically designed NOT to do. My 35 year old Sears 2/10/50 charger, however, does a dandy job at this.
 

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Drifting Alert!

What do solar chargers have to do with the dark current subject?
 

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2018 Outback 2.5i Limited, No Eyesight, No Navigation
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Discussion Starter #20
Good comment, but I just wanted to clarify something here. The high quality float/maintainer (Battery Tender, NOCO, CTEC, etc.) probably won't do the trick here unless you select a mode (varies by model) to execute this. Equalization typically requires an overcharge state, something float/maintainers are specifically designed NOT to do. My 35 year old Sears 2/10/50 charger, however, does a dandy job at this.
CTEK US 7002 can charge a 12V battery up to 150 Ah capacity.
http://a.co/6XjILyh

NOCO Genius G7200 can charge a 12V battery up to 230 Ah capacity.
http://a.co/dgcB3dy

I plan on getting one of these.
 
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