Parasitic battery drain - What is considered too high?

Car: 2017 Subaru Outback Limited
Parasitic drain: Current draw on battery with car turned off.
If the car sits idle for more than a week, it may not start. The
battery has been drained. I bought a jump booster to make sure the car
could be started when this happens. The original 380 CCA battery got
replaced with a 650 CCA. Still have the problem that the car may not
start after sitting for a week. I'm having to use the jump booster even
with the new bigger battery.
There are lawsuits against Subaru regarding their using undersized
batteries that cannot handle the load. The car can be driven for 2
hours on a trip, the alternator works, they stop somewhere and turn off
the car, return to the car in less than an hour, and the car won't
start. Since I replaced the battery with a much larger one (yeah, 380
CCA is an insult to owners in north states with real winters), the issue
with me is not with an undersized or even an old battery without
sufficient capacity to start the car. When I use the jump booster, it
is just long enough to start the car, and then it gets disconnected, so
it is not charging up the battery. Once I get the car started, it
starts fine for weeks until it happens to sit idle for about a week.
A battery load test returns a good status. It should, especially on the
new battery. That measures depth of charge, not the drain on the
battery while the car is turned off. When the battery is not drained,
the car starts fine. Plenty of capacity there. A week later, turning
the key doesn't even make the engine groan. Seems like if the car won't
start that it doesn't even try.
Does a battery load test include testing the alternator to determine if
it is putting out enough current to recharge the battery after a start?
The battery measures 12.6VDC when not running. When running, the
battery voltage measures 14.8VDC because of the alternator. However,
voltage won't tell how much current can be delivered by the alternator.
14.8VDC pushing 40 to 120 amps is a lot different then 14.8VDC pushing
into a tiny 2 mA load.
None of the interior lights are on. In fact, I flipped the switch on
the dome and cargo lights to make sure a door wasn't mysteriously
becoming ajar and the door/tailgate switch wasn't turning on a light.
I'll have to wait until a bit warmer weather arrives to disconnect the
positive cable on the battery and use an ammeter to measure the drain
when the car is turned off. I'm wondering what to expect for the
parasitic drain on the battery when the car is turned off. I thought
around 30 ma was considered the maximum parasitic drain load on a
battery with ignition off and should be good for about 3 weeks before
the battery drains too low (not dead, just not enough capacity) to start
the car.
I have an ancient analog Amprobe ammeter that goes up to 300 A but
scales down to a 40 A range. If the drain is lower, I have a digital
autoranging DVM that handles 10 A. Starting with the Amprobe, I won't
have to worry about opening a door and spiking the battery load to 2 A.
I could even test what is the active battery drain when the ignition is
turned to On but the car not started. Wonder how much that will be. In
fact, it appears some electronics are erratic when trying to capture
their parasitic drain. You have to catch them when they latch on, but
they eventually go off (and on, and off, and repeat). Apparently
turning the ignition on and off (and perhaps repeatedly) will latch them
active for awhile.
If the parasitic drain is super high, I don't relish have to wiggle
under the dash to pull out a fuse, wiggle out to check the meter, and
repeat until the drain suddenly drops. Did the dealer ever do this type
of testing looking for which circuit had the highest parasitic drain?
Obviously not since the no-start problem remained.
Hmm, I just remembered I have an OBD-2 device (OBDLink LX Bluetooth, see
formatting link
stowed in my old 2002 Legacy. Wonder if that will tell me anything about battery load, even with the car turned off. The OBD-2 port still gets power (to power the device, if inserted) with the car turned off. Its Android app has a Battery guage showing current battery voltage, but I'd need history or data logging to show how fast and when the battery got drained. Its app pages says "Log data to CSV format". Alas, the smartphone would add to the drain on the battery when the car was off, but a graph of voltage over time would still indicate how fast the battery was draining with the car turned off. If the ammeter test doesn't reveal anything, maybe the OBD-2 would.
The dealer says I should attach a battery tender (aka maintainer).
Yeah, mask the problem. Same shit they pulled for the head gasket
failures by pushing their special coolant with leak-stop goop.
Another query: how far away is far enough to where you lay or store your
key fob in your house to keep the car from sensing it? I park the car
in a disconnected garage. There could be times when the key fob is on
the kitchen table near the side door that is opposite the garage side
door. My guess is the key fob would be about 20 feet away from the car
at a minimum, and farther most of the time.
Reply to
My wife had the battery go on her 2008 Forester a few weeks ago. It was only parked in the garage 2 days but she left an interior light on. It was completely dead. She called AAA and they determined the battery was drained but weak. Would not have thought a little light left on would do this. Everything off, your much newer vehicle should not do this.
Over the years, I see key fobs vary with distance they can work. My first Subaru worked at 50 yards, a later one at maybe 10 yards and current one at least 50 yards. Hard to predict what yours might be.
Reply to
Uh-huh. Sounds like BS.
Sister has a 2017 Forester. Occasionally I hear a faint hum around the right rear fender, late at night, long after it had last been driven. Maybe a recirculating fuel pump.
Why did you specify positive? The current on the negative side has to be the same.
You used "battery tender" generically, lower-case. Excellent. After my experience with the absolutely useless 6-Volt Deltran Battery Tender Junior, I do not recommend Battery Tender.
Reply to
Local Favorite
Many years ago I left my 1985 Honda Prelude unstarted for a couple of weeks while we were on a trip. When we got home, the battery was dead as a doornail. Some weeks later I drove into the garage at night and, after the engine was turned off, I happened to notice a dim light shining on the pedals. Inspection showed that the courtesy light in a little change drawer at the base of the dashboard was still on. That was enough to drain the battery in less than two weeks. Luckily, the problem was that the switch for that light had been misassembled at the factory and I was able to correct it without going to the dealer.
The OP might want to inspect his car in the dark to see if maybe a glove compartment, trunk, or other small light fails to go out when it should.
Reply to
John Varela
I've used two 12-volt Deltran chargers for years, one a Battery Tender Plus on my vintage Mustang GT and the other a Battery Tender Junior on my 1981 Honda CB750 motorcycle, both "hanger queens". I highly recommend Deltran products.
Back to the original post: We were out of the country for a couple of weeks recently and when we returend to much cooler temperatures, my 2005 Impreza WRX and my wife's 2007 Forester startted immediately.
My Atoto A6 aftermarket GPS and entertainment head unit -- which draws a small amount of "parasitic" current so it will instantly load on car startup without rebooting the Android system -- had timed out like it was designed to without discharging the battery.
You definitely have a problem that should be fixed under the Subaru 36-month / 36,000-mile warranty. If your dealer won't tackle it and puts the problem back on you with the Battery Tender suggestion, I suggest contacting Subaru at 1-800-SUBARU3 (1-800-782-2783). Electrical problems are had to diagnose and fix; that's the dealer's job, not yours.
Good luck!
Reply to
Ben Jammin
Years ago here in northern US we had a problem with battery running down when not in use. Then the car sat outside during a light snow storm. Guess what: There was a circular patch on the trunk lid where the snow melted! The switch to turn on the light in the trunk had gotten bent so that the light stayed on with the trunk closed. Not something you could have seen, since the switch was not supposed to shut off until the lid was clear down on the weather stripping. The moral: Use all of your senses, look for anything out of the ordinary. Looking to see the light itself may not be good enough!
Reply to
Bob Wilson

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