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2000 Subaru Outback Limited Sedan, 2.5L
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163 Posts
Discussion Starter #1
Anyone ever check to see how much their battery drains on a typical day after the car sits overnight? I never really gave it much thought as long as the car started the next day, but I recently bought a Bluetooth FM transmitter which displays battery voltage when the transmitter first gets power. The unit consistently displays 10.4 volts, which seems low to me, but there's no problems cranking/starting the car. Volts are above 14 while engine is running, so alternator should be good. I'd be curious to know if anyone else monitors their battery voltage prior to the first start of the day. I figure 10.4 is either typical, my battery is telling me it's on its way out, or I have parasitic voltage draining the battery.
 

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2008 OB Limited 2.5i, Portland OR USA
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6,359 Posts
Battery voltage should be 12.6 fully charged at rest, and 13.7 to 14.7 when charging. A 10.4 rest voltage indicates a significant problem.

Since you seem to have no problem starting it, I would have the system checked with a calibrated DVM, and not depend upon what some bluetooth device registers.
 

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03 H6 OBW & 06 WRX Sportwagon
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17,711 Posts
how old is the battery? kinda seems like it has a dead cell.

parts store could test it for you but, seems like it needs replacement.
 

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'03 outback limited, '01 Outback Limited, '01 Legacy L wagon, '96 Legacy Brighton wagon
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2,257 Posts
Anyone ever check to see how much their battery drains on a typical day after the car sits overnight?

i found on my '01 OB that the drain was .154 ( if I remember correctly) amps, sitting there with nothing on ( and without the alarm system activated), so yours might be somewhere near the same. The voltage drop overnight will depend on the battery reserve capacity, as well, of course, it's overall condition.



At 10.4 volts, the car should still start, but the starter will sound like it is struggling a bit.
 

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2018 Outback 2.5i Limited Eyesight - Remote Start - Auto Dimming In/Outside Mirrors
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247 Posts
What does the transmitter display when in another car? If it does the same 10 volt thing ... then I would question the transmitter. Otherwise, I might be inclined to pop the hood and check the voltage directly. If after overnight (or a few hours of rest) you get 10 volts directly ... I would at a minimum throw a charger on it, if you have one, overnight and see if the charger can get 12.5 volts out of it. Modern chargers with all of that "smart" charging stuff they they come with now a days can bring quite a few batteries back. Otherwise, definitely get it looked at and/or replaced.
 

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I simply cannot abide useless people.
2006 2.5i and 2002 3.0 wagons.
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12,307 Posts
10.4 is seriously low.

Kaylee would often sit in a Chicago parking garage for 2-3 weeks at a time without being used, never had a battery issue with her.

Mal seems to have more of a draw from somewhere I haven't been able to trace yet. A week or so sitting while we were out of town and he barely started.
 

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2012 OB , 2017 Impreza
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3,294 Posts
Incase it was not made clear in previous postings... a healthy battery does not slowly drop voltage.


Instead, it tries VERY hard to maintain full voltage. (6 cells X 2.1volts = 12.6volts) until one of the 6 cells quits working. If the voltage drops to 10.4 ... I would assume that one of the 6 cells is not participating any longer.


FIRST: FULLY CHARGE the battery with a quality battery-charger.

SECOND: If problem persists, change battery.


NOTE: Driving the vehicle is NOT considered charging the battery.
 

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2001 VDC/SC One of a Kind
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14,475 Posts
I always suggest using the proper tool for the job at hand. When your car relies on electricity to operate, I'd rather check it with a device I know will measure correctly. Like an ammeter. Either your battery is toast or your measuring device is crap.

Voltage is a good indicator, but ampere output is most important.
 

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2018 Outback 2.5i Limited; Green/Ivory; Eyesight; Navigation
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84 Posts
I would do some looking at the Bluetooth device and its physical connection. Where does that BT attach to the car to get its voltage?
If it is attached at a place that has any length of wire before it gets to the battery, you are going to see a voltage drop due to the resistance of the wire. The same is true if the path to the battery is going through smaller gauge wire(s).....again, resistance.



Like johnre said, I'd check the battery voltage with a good digital multi meter (DMM); checking the voltage at the battery.



If you think that you have a parasitic draw, a good DMM can help with that also.
 

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2000 Subaru Outback Limited Sedan, 2.5L
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163 Posts
Discussion Starter #10
Turns out the Bluetooth device is in error. 10.4 on the device = 12.7 at the battery. I should have checked battery voltage directly when I first saw 10.4 on the device.
 
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