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2008 Subaru Outback 2.5I Limited w/VDC, HomeLink, remote start
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Discussion Starter #1
I’ve been having battery drain problems with my 2008 Outback Limited. Low mileage (65k after 12 years), as I primarily drive to and from work three miles away.

I’ve gone through five batteries in four years. I purchased a solar charger and a battery tender. It’s a pain to hook up the solar charger (didn’t hard wire, as it’s not recommended), and as I live in a condo, running a 100ft cord to top off the battery is not ideal, even on occasion.

I measured the parasitic current while parked, and it cycles from a high of 130 ma to a low of 70 ma. Cycling from high to low is roughly at a period of four seconds 0.25 Hz). I tracked the major current draw to the combination meter/integrated unit electrical circuit. With the fuse pulled, the draw is around 40 ma (still not ultra low). With the fuse in place, the 130 ma peak occurs in sync with the security indicator light flash. Not too efficient and of a system in my opinion.

With the stock battery at fairly low amp hour (ah) capacity, this current draw will drain the battery quite quickly. With say a 40 ah battery at an average of 100 ma draw and a 0.6 derating factor, that’s 10 days parked. The $300 Odyssey Extreme is rated for 65 ah, so that would help.

Is the 130 ma peak draw unusually high or normal for this model year? It in any case seems very high compared to what I see elsewhere, in other car models. Note removing fuses from the other circuits seemed to help. Any suggestions for reducing the draw?

Planning on passing this car over to a college student, and we’d like to ensure she’s not stressing over how many days it’s been since she last drove.
 

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2005 Outback VDC limited 3.0r
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716 Posts
Any aftermarket alarm/remote start/stereo or amp installed? Are you also taking short drives that don't fully charge the battery? Lots of shut off/restart? Iirc some people say anything under 200ma is good, others say 100 or 50. Are the keys kept in close proximity to the car?(no hidden spares on the car?).
 

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2008 Subaru Outback 2.5I Limited w/VDC, HomeLink, remote start
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Discussion Starter #3
Good questions. Nothing aftermarket. The alarm/remote start/stereo were all Subaru OEM components that came with the vehicle when purchased. Definitely plenty of short drives, so that is an issue. BTW, I did measure the alternator charging voltage and it varies between 14.1 and 14.3 V, so that all looks good. 100 ma still seems high to me (my average current draw if you take into account security light on state averaged with off state).

Page 8 of this tech paper states that typical draw is 15 to 40 ma, with 150 ma indicating an issue: https://aamcouniversity.com/wp-content/uploads/sites/7/2019/08/LBT-270-MAN-PARASITIC_DRAIN_WEB_V1-41126.pdf?highlight={search_term_string}

Of course those current draw values are not Subaru specific, and it's uncertain if those are truly typical draws.

No hidden spares, and keys and remote start fobs are kept in the house, often about 30 to 50 feet from the car. I did pull just about all the fuses in both fuse boxes, so if there was a circuit dependent on proximity of a fob, it would have dropped the current, I suspect.
 

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I tracked the major current draw to the combination meter/integrated unit electrical circuit. With the fuse pulled, the draw is around 40 ma (still not ultra low).
Note removing fuses from the other circuits seemed to help.
Some fuses are identified in the Owners Manual by only one of several circuits it powers. Consequently, it might be helpful if the fuse could be better identified (location, number, amperage, a photo) so that this possibility can be checked in the wiring diagrams.

The 40 ma is, to me, still seems high. Presumably there would have to other fuses that would reduce that even further.

On my 07, with everything off (no remote start) and after sufficient time for all systems to go into full standby mode (important!), the dark current is not more than 10 ma. (EDIT: Clarification: Less than 10 ma. is the base level; with the security light flashing, the current pulses higher, but not beyond 15 ma max.)

The Subaru maximum for dark current back in gen3 days was 150 ma, but as of 2010 or so, a new spec of ~70 ma was issued (although I think that might have been meant more for the later generation).
 

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2005 Outback VDC limited 3.0r
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716 Posts
The best bet might be to just get a battery disconnect switch. Even if you get the draw down to 40ma, it sounds like the car will still sit for long periods of time. You can wire one up and all the student has to do is open the hood and flip a switch.
 
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