Noobie: How to safely disconnect battery?

[1013mm]

How do we safely disconnect the car battery and connect it back? I'm totally embarrassed by asking this...

[JohnL135I]

Open your trunk, lift up on the panel that covers your battery. use a 10mm socket to loosen the bolt on the negative battery terminal, pull the terminal off the battery post and put something between it and the post (microfiber towel will work).

To reconnect, reverse directions.

[Itanius]

I can't blame you for asking, John. All those wires and plastic pieces they have in the battery compartment can be a little intimidating at first. The first time I looked in there I had a "WTF?" bubble floating over my head.

[onefastman]

If you work quickly you might be able to save your settings.

[1013mm]

which one is the negative?! =X

[BSM 135i]

Originally Posted by jzhang

which one is the negative?! =X

the one with the (-) and is black

[and 1]

any ideas how to prevent the sparking when reconnecting?? i can't see that being a good thing

[rsjean]

Originally Posted by and 1

any ideas how to prevent the sparking when reconnecting?? i can't see that being a good thing

You can't. But you can be real fast and it does nothing bad anyway. Unless you are in a garage with a very bad natural gas leak.....

On a related topic, any ever heard of the power port (before known as cigarette lighter) cable with a 9 volt battery that you plug in while you work on electrical etc with the main battery disconnected and it keeps you from losing your settings???

[spang135]

My neg (-) cable is brown not black just throwing that out there

[Taymaishu]

Remember that when taking off the battery, - first.

When re-connecting (powering the car), + first.

Easy way to remember:

When minusing the terminals, - first.

When applying the terminals, + first.

easy!

[1013mm]

ok guys thanks for all the help, it was simple... LOL

[timhatimay]

Originally Posted by rsjean

You can't. But you can be real fast and it does nothing bad anyway. Unless you are in a garage with a very bad natural gas leak.....

Keep in mind that when batteries charge they give off Hydrogen gas which is very explosive. If it is not a well ventilated area, or there is a proper mix of gas (ie LEL), then the spark could be very dangerous. Maybe I'm paranoid, but I always open the compartment for a few minutes before I disconnect and reconnect. It is something to be aware of.

Tim

[Lester]

German batteries don't give off hydrogen gas, they learned their lesson from the Hindenburg.

[TheRustler]

Lead Acid batteries are sealed. That would be a serious fire/explosion risk if that was the case. I've disconnected my battery probably a dozen times (- only). It really doesn't matter what side is disconnected. In electrical engineering terms, all you have to do is open the circuit (disconnected at least one terminal) to remove power.

Also, I would not recommend plugging in one of those cigarette battery starters when performing maintenance. The computer could be powered. Its best to just be safe and reset the clock.

[timhatimay]

Lead Acid batteries are sealed. That would be a serious fire/explosion risk if that was the case. I've disconnected my battery probably a dozen times (- only). It really doesn't matter what side is disconnected. In electrical engineering terms, all you have to do is open the circuit (disconnected at least one terminal) to remove power.

Not all lead acid batteries are sealed. Also, I believe the battery will still give off hydrogen if overcharged, or charged too quickly. In a sealed battery, if there is any hydrogen formed, it should be recombined into water within the battery, BUT it still can escape through an escape valve should there be an excess formed (to prevent explosion of the battery from internal pressure). Upon second thought this would be more rare in a sealed lead-acid (e.g. car) battery, but can still happen. Opening the circuit is the important idea for disconnecting the battery, but from a safety standpoint, its important to remove the negative. Otherwise, you still have the common at all metal on the car, and a slip with the wrench or your self causes a short. Which wire to remove in a live circuit can be an important distinction if you ask me...but like I said before I'm paranoid!

Tim

[jeremyc74]

Originally Posted by TheRustler

Lead Acid batteries are sealed. That would be a serious fire/explosion risk if that was the case. I've disconnected my battery probably a dozen times (- only). It really doesn't matter what side is disconnected. In electrical engineering terms, all you have to do is open the circuit (disconnected at least one terminal) to remove power.
.

Lead acid batteries ARE NOT sealed, and they absolutely pose an explosion risk if they've been deeply discharged in an area that isn't well ventilated. The battery compartment in these cars is vented for that very reason.


From an electrical point of view it doesn't matter which terminal is disconnected. The reason you disconnect the (-) first is because if you're doing the (+) first and hit the chassis or other electrical equipment with the wrench you're going to create a short.

Removing the (-) first is the safest way to do it. Once that's disconnected the chassis is no longer an issue if you touch it while removing the (+).

[techS54]

Wow fellas, look at the argument you got into over a simple battery disconnection issue :-)
JZHANG just one tip for you; the IBS sensor (part of your charging system/electrical system monitoring) is integrated into your negative cable and is very sensitive. Make sure when reconnecting the cable to torque the nut to 15nm.

[jeremyc74]

Originally Posted by techS54

Wow fellas, look at the argument you got into over a simple battery disconnection issue :-)
.

Who's arguing? There was some inaccurate information given, and it's been corrected.

[black e]

anyone swap the stock battery for a lighter battery like a braille?

[JHZR2]

There are sealed (valve-regulated lead acid) AND unsealed. More and more are sealed, but just because the battery is inside the vehicle and not underhood does not guarantee that it is a sealed variant.

And even "maintenance free" sealed batteries are not the same. Many of them still have an active vent.

Since I do not hae my car yet, I cannot say what the car comes with.

The best way to prevent sparking is to minimize the electrical load upon connection. This may be kind of hard, but at least try to ensure that all lights, charging devices, etc are not present. Beyond that, it isnt good but it isnt bad for all practical purposes.

[esky]

Originally Posted by jeremyc74

Who's arguing? There was some inaccurate information given, and it's been corrected.

LOL
:lol

[JimD]

Wikipedia describes certain car batteries as being Valve Regulated Lead Acid (VRLA). They normally recombine the hydrogen and oxygen generated as the battery is discharged back into water. But sometimes the battery is charged or discharged too fast and the valve opens to prevent the pressure inside the battery from getting too high. This battery would normally be described as "sealed" but it isn't totally since the valve can open.

I don't know that the VRLA type is what bimmers have but it may be. But that would not eliminate the chance of there being some hydrogen around when you are working at the battery. But it is never very likely and is even less likely with the VRLA battery.

As a practical matter, opening your trunk as you gather tools to do the job would probably give any hydrogen a chance to be diluted to the point it would not burn or explode.

I do not worry about it.

Jim