One of my late wife’s cars did that a time or three. Absolutely baffling. We eventually caught it in the act. The battery was not the problem.
Somehow after you parked the car and closed the doors, occasionally the interior dome lights would stay on indefinitely, rather than powering down after a minute or two as designed. Which sustained operation would reliably drain the battery to flat in about 36 hours. She was WFH in those days, and I generally drove when we went places together, so her car sitting there in the garage with the dome lights draining the battery sight unseen was an easy oops.
I did something similar to my car about 3 years ago: I had an OBD-II dongle plugged into the port to do some logging and troubleshooting. It’s a mild PITA to stuff the plug into the socket, so after one session I just left it plugged in, intending to come back to it tomorrow for more. I came back to a stone dead car. Unexpectedly, the act of leaving the dongle in there kept most of the car’s electronics alive after I’d locked the doors. Which locking usually shuts down the car to as “off” as it gets. Oops. Lesson learned.
My problem was slightly ambiguous, but the repair shop showed me a diagnostic chart where it appeared that the alternator was acting up intermittently. I was a bit skeptical because the battery seemed to have a good charge the last time I started the car some days prior, and there was no warning light suggesting an alternator failure. In the end, I had them go ahead with replacing the alternator and in the process they also replaced the battery under warranty, so the exact cause is inconclusive but I don’t care since everything works. Besides, who am I to question a scientific-looking chart with squiggles on it?
The kind of battery drain you’re describing can be a bitch to track down, especially if it’s not caused by a light or some other visible cause. I once had my battery substantially discharged but still able to start the car after the trunk lid had been accidentally popped, because there’s a light in there.
Strange. A VW Beetle was my first car, and I don’t think I ever heard the term “frunk” at that time. Though I suppose owning the car wouldn’t necessarily make me more privy to terminology about it. But to me it was simply “the trunk” because the Beetle had no other.
In the 90s a friend and coworker had a classic Beetle (purple and white, it was gorgeous) and he called it a frunk.
But that might have been more obscure than it is today. It’s not like I heard that term a lot from everyone. Maybe it’s a coincidence.
Merriam-Webster, for example, says the idea of a “frunk” isn’t new (and even uses the same example I did of an old Beetle) but at least implies that the term itself has only become popular in the past handful of years.
So again, maybe a coincidence that I knew a guy years ago that called it that. He was the only person I knew with such a car so I thought that other people who owned a Beetle called it that too.
ETA: Here’s an article almost 8 years old discussing a frunk but it is also in reference to a Tesla.
Prior to the existence of Teslas, the cars in the USA with frunks were VW Beetle, Chevy Corvair, Porsche 911, Porsche 914, and … crickets.
Only the 911 was built past the 1970s and although everyone knows what a 911 is, damn near nobody drives one; they’re not exactly common like Toyotas. And as such darn few people have reason to refer to their frunks.
Tesla is the first mass market car sold in the USA with a frunk in the last few decades. As such, it’s unsurprising that the term has now burst on the scene and folks without some pre-existing connection to the term assume it’s brand new. Because it’s new to them.
A common Jeep problem* (AMC era). Trick was to install a one-way diode (?) in-line with the connecter to prevent the alternator from sucking the battery dead overnight while you were drinking beer around the campfire. Never quite understood the workings of this failure, but the cheap install worked.
Just spitballing, but I’d bet it was leakage current in the alternator equivalent of the old DC generator’s voltage regulator. So there it sits being a phantom load all day and all night just like a trunk or dome light left on. And while the engine is running, the VR still does its job well enough and the small ongoing load represented by the leakage current is lost in the sauce of overall alternator output and vehicle current draw.
Yeah, had to be something like that, because the alternator tested good/functioned as it should. Whenever you weren’t drinking beer around the campfire.
Very interesting. I now remember the tech mentioning something about a diode within the alternator being shot. I didn’t know – and nor would it ever have occurred to me – that in addition to maybe not charging properly, the alternator could have been a parasitic drain on the battery. That definitely matches the symptoms, because after being jump-started and driving around briefly, the battery had enough juice to start the car on its own, so it wasn’t totally shot but had been drained by something, and that something is now gone.
I’m glad they were kind enough to replace the battery anyway, only because being drained totally flat would probably have limited its life expectancy. It wasn’t a cheap fix but was well worth it. They also said they re-fastened some loose wiring that had been flapping around down there. The car is no spring chicken – it will soon celebrate its 20th birthday! The year after that, it will be old enough to drink in even the most restrictive provinces and states.
If an alternator output diode fails by going open the alternator puts out half the juice. Full voltage for one half of the sine wave as it spins, and zero volts the other half as the voltage being created can’t get past the open diode. The end result is a lot less charging current, but almost certainly still enough to keep the alternator failure idiot light off. So, especially in winter with high loads for heaters and lights plus short trips you get a battery that is just barely getting charged with each use. Which counterinituitively manifests as a brick wall failure in having and holding enough charge to turn the starter once things get bad enough. You’ll get a couple of half-hearted semi cranks and then nothing but useless clicks. Then real quickly nothing at all.
There are other diodes in the regulator circuit, but those are probably not the ones your tech meant.
If I might hijack this thread about alternators and frunks with some Elon Musk news, he’s apparently decided that neglecting a mere 11 children wasn’t agile or hardcore enough.
I’m starting to think he expects his kids to one day battle to the death for his legacy like Byzantine princes or the pagan kings of Norway.
Also; do we know for a fact that his babymama didn’t change the spelling of her name because Elmo couldn’t figure out “Siobhan”? It feels like the kind of move he’d pull.
It would not surprise me in the slightest to learn that they have extracted thousands of eggs from each of his wives / GFs, and vast numbers of them have been linked with his sperm to form now-frozen embryos. At the right time 10,000 micro-Elmos will be implanted into an army of paid surrogates and soon the future master race will be born.
That incredibly fecund King dude from the middle ages (whose name escapes me as my edit window times out) contribution to the future human family tree will be as nothing compared to the mighty Elmo!
