What's up with the cigarette lighter?

I just bought an 06 2WD, 2-door, 2-seater (ST?) with the 6-speed manual transmission. It's a shame it's not a 4x4, but it carries surfboards just fine. Anyway.

There are two outlets in the dash. One on the right has a flap cover and is powered all the time. No problems here. The one on the driver side has an actual cigarette lighter in it (I haven't seen one of those in ages). According to the manual, this one is only supposed to be powered when the ignition is on.

Here's the problem: I left a USB socket in the cigarette lighter socket (nothing plugged in) and came back an hour or so later and the battery was dead! What gives? Even if the outlet was powered, the tiny LED on the USB socket shouldn't kill a heavy duty truck battery in an hour, right? I did notice that the LED was flickering (it's usually either on or off) while the ignition was off, which is what caught my eye and made me try to start the truck.

Any ideas?

I doubt that would be the problem. I have a charger plugged in on the passenger side and I never unplug it. It has a tiny led, but I don't think it would effect the battery at all.

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I've been testing with a different USB socket (no LED on this one) and so far it hasn't killed the battery.

So it seems like USB socket I was using before was causing the problem. This is strange because it is a quality device (Belkin) and has never caused a problem in many other vehicles that I've used it in. Even so, how would it be drawing so much power when the outlet itself was supposed to be off? Very strange.

Check the owners manual if you have it.... I know on my challenger you can change the fuse position on one of the outlets that will change it from ignition on only to powered all the time. I know people on the challenger forum had trouble with led chargers draining the battery if it was in the powered all the time position.

stimpy433 said:

Check the owners manual if you have it.... I know on my challenger you can change the fuse position on one of the outlets that will change it from ignition on only to powered all the time. I know people on the challenger forum had trouble with led chargers draining the battery if it was in the powered all the time position.

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I've seen that option, but it isn't mentioned in the manual I have. I have confirmed that anything plugged into the socket will indeed stop charging when the ignition is turned off, which is the desired effect. It's just strange that the other USB charger was able to kill the battery when the socket was supposedly off.

It is pretty unlikely that little USB charger is pulling enough power to kill your battery but it is easy to find out for sure if it is or not.

Get a multimeter and set it up to read current draw with your key out of the ignition and everything shut off, with the charger in question plugged in to that outlet. If the reading is abnormally high, more than around 50 milliamps, have someone unplug the charger while you watch the meter. If it plummets, then it could be your issue.

Keep in mind that to kill a battery the size of the one in your truck in 8 hours, there would have to be a constant draw of like 15 amps. This is a huge amp draw and will be easy to find by using the method above. If that charger was drawing 15 amps with nothing plugged into it, there would probably be some smoke involved.

justin13703 said:

It is pretty unlikely that little USB charger is pulling enough power to kill your battery but it is easy to find out for sure if it is or not.

Get a multimeter and set it up to read current draw with your key out of the ignition and everything shut off, with the charger in question plugged in to that outlet. If the reading is abnormally high, more than around 50 milliamps, have someone unplug the charger while you watch the meter. If it plummets, then it could be your issue.

Keep in mind that to kill a battery the size of the one in your truck in 8 hours, there would have to be a constant draw of like 15 amps. This is a huge amp draw and will be easy to find by using the method above. If that charger was drawing 15 amps with nothing plugged into it, there would probably be some smoke involved.

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I agree.
Maybe the brake lights are staying on. If you have any high intensity interior lights, staying on that might do it, too.

Could also be a weak battery. Last year I drove to Mcdonalds to grab something to eat, turned the truck off for less than 5 mins, and it was really weak when I tried to start it. Connections were good. But battery was weak. It was fine after that for a few weeks. Then randomly died a few weeks later.

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Thanks for all the input. The battery is strong and less than a year old. No other lights, accessories, or anything else were on when this happened nor during subsequent tests. I don't have my multimeter handy to test anything properly, but if I ever get around to it I'll post the results here.

It has been a couple of days since I plugged in the new USB socket, and there has been no issues. Battery is still strong. The outlet powers off when the ignition is off. Everything is working as desired. If anyone is interested, it's an Aukey dual USB. Sits almost flush with the dash and doesn't have any annoying LEDs.

As for the problem the killed the battery the first time. My best guess is that the other USB socket was somehow causing a short somewhere. The device itself draws almost no power even with the LED, so there's no way that could have drained the battery in such a short time. If it was, it would almost certainly have melted or caught fire. Perhaps the shape or design of this particular USB outlet is somehow making an unwanted connection behind the dash, completing a circuit and draining the battery.

The only indication that something is awry is that the LED on the USB socket is usually either on or off. Nothing in between. On if powered, off if not. When plugged into the cigarette lighter with the ignition on, the LED would be on and anything plugged in would charge. Turn the ignition off, and instead of going out, the LED would start flashing rapidly.

TL;DR: the cause of the initial problem is still a mystery, but I have found an acceptable solution.