Car Battery Conundrum
October 5, 2012 3:28 PM   Subscribe

I have a brand new car battery. My car has some issue that is (still) draining the battery, after I already had a mechanic look at and fix what was supposedly the issue. What can I do so that my battery doesn't go dead and get ruined over the winter while the car is idle?

From what I could see online, you can't just take the battery out or it will go dead. It's a brand new battery - been in the car less than a week. The car starts up, but as each day goes by, it takes slightly longer (.5 more seconds) to start up. Something is draining the battery. Whatever it is drained the previous battery so completely that it ruined it and made it unable to be recharged (and multiple aaa drivers said that). I thought I had the issue fixed and some warning lights that were on are now off. The door light doesn't stay on anymore even after the door is closed. But apparently there is still an issue of some sort that is draining the battery.

So I have a brand new battery now (I put it in a week ago), and I don't want that to happen again.

I can't drive it around (it is in a safe parking place on a street), but I can start it up every few days. It is not near an electrical outlet. In searching, I also read that various car parts could be damaged if the battery is removed for extended periods of time.

What can I do so that the battery doesn't go dead?
posted by furious to Home & Garden (17 answers total) 1 user marked this as a favorite
You should be able to find a "kill switch" that will safely disengage the battery without harming anything. (though if your stereo has an anti-theft code, you may need to re-enter it each time.

Sitting disconnected shouldn't harm a modern car battery. (they sit on shelves at auto part stores for months at a time, after all.)
posted by ShutterBun at 3:39 PM on October 5, 2012 [1 favorite]

Ask your mechanic about the alternator--that's what repeatedly killed our batteries, and the first mechanic we took the car to missed it somehow. And it's not heinously expensive (it cost us about $350, I believe)--although if that's the problem it's not like you have a choice about whether or not to repair.

Sorry I don't have an answer to the more immediate question. Good luck with this!
posted by supercoollady at 3:44 PM on October 5, 2012 [1 favorite]

(it's the kind of thing they use on boat batteries, which routinely sit unused for months at a time)
posted by ShutterBun at 3:47 PM on October 5, 2012

It isn't the alternator (had that tested), but I will look and see if there is a switch!
posted by furious at 3:57 PM on October 5, 2012

By "find a kill switch" I think ShutterBun meant "have a kill switch installed".

Finding the source of battery drain can be a challenge. Keep in mind that the battery is getting heavily drained every time you start the car, though, and then the alternator charges it back up. So there's a big difference between the situation where you leave the car for a few days and then the battery's dead, and the situation where you drive the car a lot and then the battery's dead.

One thing you(r mechanic) can do if it's the "drains when the car's not in use" problem is put an ammeter on one of the battery leads, observe the current, and pull a fuse at a time until it stops.

I can't entirely tell from your description if you're planning on putting the car away for the winter, but if you are, you can pull the battery. But a battery in a car left idle for a while will suffer a little regardless. Motorcyclists who put their bikes up for the winter use a Battery Tender to condition their batteries while they're sitting unused, either on the bike or off. There are Battery Tenders for car batteries too.
posted by mendel at 4:09 PM on October 5, 2012 [1 favorite]

Oh, by "find" I meant "purchase." (they're not standard equipment)
posted by ShutterBun at 4:10 PM on October 5, 2012

From what I could see online, you can't just take the battery out or it will go dead.

You can test the situation with a cheap voltmeter. The harbor freight people will sell you one for under $10. You'll also want some alligator clamps (or a friend) to hold the test leads in place while you work.

Disconnect your positive battery wire and hook up the voltmeter (on DC amps) from the positive terminal on the battery to the positive battery wire. If all the lights are out there should be maybe 100 mA being drawn (that's just a guesstimate). OK, now pull fuses one by one, noting which ones cause the number to drop. The ones that caused a big drop are your suspect systems.

The problem with bench testing your alternator is that it still might not be charging the battery even if it passed the bench test with flying colors. This is because the field terminal might not be receiving voltage under your hood. No field - no charge. The system should be running at 14.5 volts when the car is running. If a cheap volt meter across the battery terminals while the engine is running says 12 v, you're probably not charging the battery while you drive. (MIND THE FAN WHILE YOU CHECK THIS!)

Heh. On preview, what Mendel said.
posted by Kid Charlemagne at 4:12 PM on October 5, 2012

Oh, okay, thank you. I think I'll just take the battery out and take my chances with any other issues until spring. I saw in searches that I should get fuel stabilizer and put that in. Do I need to do anything special in storing the battery? I plan on storing it indoors for winter, but does it matter? Could I just put the battery in the trunk?
posted by furious at 4:15 PM on October 5, 2012

Just disconnect the cables and leave the battery in the engine compartment or wherever it normally is. No sense hauling it in and out.
posted by Sternmeyer at 4:26 PM on October 5, 2012 [1 favorite]

Is getting it checked by a different mechanic a possibility? Because if you've changed the battery and checked the alternator, that seems like a good idea.

Alternatively: what kind of car do you drive? I have a 2003 PT Cruiser, and there's a known problem where Cruisers sometimes develop a short in the wiring of the multi-function stalk (the handle that controls the fog lights), and even though you've got the lights turned *off*, those fog lights are *on* and draining power..... perhaps you have something similar.

Oh, and you say the car is parked on the street --- you might check, but a lot of areas limit the amount of time a car can stay in one place on a public street: in my area, after 72 hours (3 days) you risk tickets and towing.
posted by easily confused at 4:31 PM on October 5, 2012

Okay, thanks. It's not better to store it indoors during cold winter months?
posted by furious at 4:31 PM on October 5, 2012

furious: "Okay, thanks. It's not better to store it indoors during cold winter months?"

It shouldn't matter. The key here is to reconnect your battery once a month and go for a 30 minute drive, presuming your alternator is actually working. If it continues to be a problem, you can buy a deep cycle battery like an Optima Yellow Top that will better tolerate being drained if you leave it to sit for too long.

I feel for you. I just got rid of a car because I didn't feel like digging deep under the dash to replace a broken fan relay that would keep the cooling fan running after turning off the car, draining the battery within a day or so. It was intermittent enough that you could walk away with the fan off and all of a sudden it would just turn on for a while, maybe foreverish. Electrical problems are the worst.
posted by wierdo at 4:41 PM on October 5, 2012

What you want to do is bring it inside and hook it up to a float charger. One of these should be very inexpensive.

You don't want to leave it outside all winter just disconnected, since lead acid batteries self-discharge at about 4% a week.

As for diagnosing the problem, what you need to do is hook an ammeter up in series with the battery and the car, and see if there is any draw. There will be some small draw for the radio, but you can look that up and see what it is supposed to be. If the draw is much larger than that, then you start disconnecting fuses until the circuit with the draw is identified. Repair from there.

If there ISN'T an abnormal power draw with the car off, then your alternator is bad. It could be overcharging the battery, slowly ruining it. Or it could be testing fine at idle, but showing lower volts at speed.
posted by gjc at 5:29 PM on October 5, 2012

You might want one of these.
posted by dudeman at 9:26 PM on October 5, 2012

look on ecomodder for the kill switch mod
posted by jago25_98 at 4:00 AM on October 6, 2012

It could well be that the alternator is ok, but the system itself isn't adequately charging the battery as you drive. You say the mechanic checked the alternator, but did he do a complete charging system check?

You don't say what kind of car this is, or whether you have any aftermarket items (like a sound system) installed. An incorrectly-installed aftermarket sound system or alarm system can cause a power-draw even when the car is off, draining the battery. Heck, on older VWs, I've seen accounts of batteries drained because the owner left a phone adapter plugged-in (VWs are a special case, as the older ones were utter crap throughout)

You shouldn't have to resort of removing the battery or installing a kill switch. Something is amiss with your electrical system and you need to have the complete system checked.
posted by Thorzdad at 6:06 AM on October 6, 2012

Sounds like it may not be charging. The alternator may function but there may be something that prevents a charge getting to the battery. A multimeter at the battery posts should show 13-14 volts when the engine is revved.
posted by sammyo at 3:38 PM on October 6, 2012

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