It’s a bit of a PITA, but I think the best method for measuring the residual current draw is the following:
Install a battery disconnect switch. Something like this or this.
Close switch, start car, and drive it around for a while.
Turn off car.
Attach a 1 Ω resistor across the input leads of your digital voltmeter.
Measure voltage across battery disconnect switch. It should read 0 V.
While still measuring voltage across battery disconnect switch, open the switch. Record voltage. If, for example, the voltage is 80 mV, it means the residual current draw is 80 mA.
Using this method, all the electronics in the car remain the proper state.
I have a new full spec VW cc with all the gizmos that Vw offered. I have also just returned from a two week holiday and my car started no problem.
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Yeah, I have one.
They are not great for measuring tiny currents - too much drift and sensitivity to external magnetic fields. A shunt is the way to go.
I have a cheap $40 DC clamp meter that I have used to measure current to LEDs at less than 20 milliamps. It has no more than a 2-3 milliamp drift if properly zeroed before use.
I have that meter, too.
I have found that it can detect current down to 1mA, but that the drift is pretty bad. If you zero the meter, and then move it into position, it will read several 10s of mA by the time it’s in place.
It seems to me that the dealer ought to be doing all this measuring of current draw. He should have the proper equipment and the expertise to do it.
But I have a similar story. A woman I know bought the same model car I did in 2007, same dealer a couple months later. In part because I was so happy with it. Same story. Her battery kept going dead. The dealer could not figure out what was wrong. They changed the battery, looked at the wiring, etc. Finally she bought a gadget–it was called something battery brain–that physically disconnected the battery when she parked. She cannot use the radio (which has to be reset when the current goes off (an antitheft device), but she has had no more problems with the battery. But I blame the dealer who should have been able to track it down and fix it.
I leave my car unused for three weeks every winter while I go off the Barbados. Never had the slightest problem starting it when I returned. It is in a garage that is heated enough to stay above freezing.
I made the mistake of leaving an iPod plugged into the car when on a trip. The car would sit for several days and I often had trouble getting it started until I realized what was happening. This was an old iPod with a nearly dead battery, so it was always trying to top itself up. Some crappy cigarette lighter/USB adapters or even charging cables that have indicator lights on them could be another culprit.
I am assuming your car doesn’t have proximity keys or the more advanced types of alarms and keyfobs. Or anti-theft recovery or communication features like Subaru Starlink which use the cell network.
One suggestion that may help the OP is to move the keys to the other side of the house and away from the car if at all possible. If a proximity key is within even marginal range of the car it will prevent the system from going into sleep mode.
If a battery tender isn’t possible you can also try disabling fob communication and sensors when parking for a long time which is covered in the manual.
70 mA drain looks typical for Subaru when in sleep mode, and looking at the battery it uses it has ~46 AH before it is unable to start the car (assuming 10.5 v) should last for 28 days. But if the key is too close it will fail earlier, and the techs will never detect that because they keys will be a lot farther than 30’ away.
One option is to try putting the unused keys in a static bag and see if the problem goes away.
It sounds like you might suspect a conspiracy of cheapness on the part of the automakers. While costs in that industry are very tightly controlled, they may not be controlled in the way you imagine. Multi-year warranties mean that the manufacturer is on the hook for replacing flaky batteries, and ones with marginal capacity get replaced a lot more than adequate batteries. This itself costs money and hurts published reliability rates.
Still, in the process of specifying the battery for any given car, someone definitely evaluated the battery-capacity-vs.-warranty-replacement curve. Excess capacity costs money up front, but there are additional hidden costs to both the manufacturer and the owner. A bigger battery weighs more and may require a bigger, heavier alternator, which in turn requires more parasitic engine power, etc. The increased mass and engine drag then consume more fuel, which is bad for both car manufacturers and car owners.
About tires: your dealer is truly mistaken. OEM tires are built to higher specifications than replacement tires. They sometimes use softer tread compounds than aftermarket tires, which can make them wear faster, but that’s a feature, not a bug: softer compounds mean shorter stopping distances. But even softer compounds wouldn’t cut tire life in half as your dealer claimed. An OEM tire might wear out 5%-15% sooner than the aftermarket version of the same tire.
Tire manufacturers have incentives to make their OEM tires reasonably long-wearing. For example, soft compounds hurt fuel efficiency, which OEMs prize. Also, most consumers buy replacement tires of the same brand as their original tires. If your OE Goodyears wear out “too fast” in your judgement, you’re likely to switch brands to get better wear.
I’m a mechanical engineer, and I first learned this about higher-quality OEM tires from another engineer who works with tires at General Motors. However, I was able to find a real cite as well. To wit:
Thanks. I thought about moving the key away. But two of the times this happened was in an airport parking garage. The key fob way 1500 miles away.
Yep. I’m just not sure they are doing it. Do to life, etal. I have not talked directly to this particular dealer. In fact, when my Wife went to pick up the car, the service desk said they where about done with it. Nope, they got two cars with the same problem mixed up. My Wife’s car had not been touched yet. So, my confidence in these guys is not great. That dealership is only 30 miles away. The next closest one is 100 miles away.
I did buy a multi-meter yesterday, and watched some videos on how to test it. Looks pretty simple, but I have not had time to do it. Perhaps next weekend.
Some fine bullshit artistry there. Have her ask the dealer if they manage to drive every single new car on their lot once every few days. Have her ask how often the dealer has to jump-start a new car before a test drive.
And what about the cars that are left in airport parking lots for weeks at a time? I would expect to see a LOT of people getting jump starts if needing to start new cars every few days was the new norm.
Forgot about that one. Plenty of people including me, take 2-3 week vacations during which their car goes untouched in a long-term parking lot at or near the airport.
You may need to abandon the dealer route and find an independent garage known for handling electrical gremlins. Had a friend with a car that would run down over the weekend if not driven, and the dealer couldn’t figure it out. She took it to a shop with a good reputation and they found an issue with the antilock brakes cycling on randomly while sitting, which draws a lot of juice.
