I need to disconnect a car battery.
Does it matter if I disconnect negative, then positive? Or positive, then negative?
Always negative first. Make damned sure it’s not touching anything before you disconnect the positive.
So after disconnecting the negative terminal, I have to hold it in the air while disconnecting the positive?
Just bend the cable away so it doesn’t touch anything.
disconnect the grounded terminal first (negative for USA and Canucks). bend it down on the side of the battery so that it can’t flop down and retouch that terminal.
Once disconnected, the negative cable can touch anything at all, except for the negative terminal of the battery.
Gah!
Another spammer.
Reported.
Here is WHY you should disconnect the negative first- the negative cable connects to the body so it is grounded. If during the disconnect process (negative side) your wrench hits a ground surface, it makes no difference. Once the negative is disconnected and you start on the positive terminal, it is not possible to short a wrench to ground. Just be careful to not short across the terminals. Shorting the battery out will cause nasty sparks and the possibilty of an explosion. And when you reconnect, start with the positive terminal for the same reason. Everyone is being emphatic here because you REALLY don’t want to be anywhere near a battery explosion.
If you are just disconnecting the battery because you don’t want it to go dead on you, you can just disconnect the grounding cable instead of both. I do this every winter with my RV. If you’re actually removing the battery, then see the above posts.
If it being disconnected for storage as mentioned by Chef guy, you might consider a quick disconnect terminal adaptor. Just turn the knob and pull it apart.
My Freshman year I became friends with a guy in my dorm who had lost an eye and his good looks to a battery explosion. About the only way to cause one is to charge a battery in an enclosed space creating an explosive concentration of gas, then strike a spark. If you’re out in your driveway with the hood up don’t sweat it, just be careful and wash the battery residue off your hands before taking a leak…
Bolding and underlining is mine.
Very bad advise! If your car has been run recently, it can have the highly explosive hydrogen gas around it. Think The Hindenburg!
I have had a battery explode after the car had sat for 30 minutes after a long trip in a driveway. My wrench slipped and contacted both the positive cable and the negative cable at the same time. BOOM! Acid in my face and on my shirt. It was very unpleasant. I do not recommend it. I hosed myself off, took a shower and changed all of my clothes. My glasses saved my eyes, but I had sensitive skin on my face and throat for about one week.
I immediately soaked my clothes in a large tub of water with a large box of baking soda dissolved in the water. The clothes were washed within 30 minutes and they all had holes in them.
I had to buy a new battery, new clothes and repaint the engine bay. It was a painful, costly lesson. I now use black electricians tape and wrap the other 1/2-3/4 of the wrench I will be using to remove the battery cables from the battery. This way the wrench can not arc and cause a spark.
Slowlearners other advice on washing your hands is very good! Do this.
IHTH, 48.
acid damage to clothes and skin/eyes is instantaneous. you might limit the extent of the damage to a slight degree, i.e. unreacted acid on something can spread to undamaged areas and react. safety glasses might look geeky or be a bother but there is no better value in the world. not only chemicals but brushing corrosion of clamps and terminals can send parts flying.
also more common than explosions is melted metal. if you short out the battery (easily caused by not disconnecting the grounded side first (negative for USA and Canucks) or not making sure the wrench doesn’t touch both terminals by any path or means) then you might melt part of a cable, clamp, terminal or tool.
Even if the battery doesn’t explode, well, I once was removing a radiator fan, and after carefully disconnecting the battery, I then began the task of draining the radiator, removing the grill, etc., and carelessly laid a wrench aside-- right on the battery. It connected to both terminals, shot up in the air, hit the hood, and came down on my head, making a scary electric buzzing sound, and lots of banging.
In the end, no real harm, but I learned my lesson. I cover the battery terminals with caps designed for just that when I’m working on the car, and I FREAKING PAY ATTENTION to where I put my wrenches.
Correct; once you remove the cable from the battery’s negative terminal, just make sure nothing comes in contact with the battery’s negative terminal.
So to summarize, do the following to remove battery:
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Make sure all electrical loads are off (key is in the off position, all lights off, doors shut, dome light off, trunk shut, nothing plugged into 12 V receptacles, etc.). This will minimize sparking at the positive battery terminal during step 4.
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Put on safety goggles.
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Disconnect cable from battery’s negative terminal. When doing this, be very careful the wrench does not come in contact with the battery’s positive terminal. If you want to be extra cautious, temporarily wrap/cover battery’s positive terminal with electrical tape before doing this step.
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Disconnect cable from battery’s positive terminal. When doing this, be very careful the wrench does not come in contact with the battery’s negative terminal. If you want to be extra cautious, wrap/cover battery’s negative terminal with electrical tape before doing this step.
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Remove battery from vehicle. Do not place it directly on concrete, else it will quickly discharge. (Just kidding!)
When reinstalling the battery, -
Make sure all electrical loads are off (key is in the off position, all lights off, doors shut, dome light off, trunk shut, nothing plugged into 12 V receptacles, etc.). This will minimize sparking at the negative battery terminal during step 4.
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Put on safety goggles.
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Place battery in vehicle.
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Connect positive cable to battery’s positive terminal. When doing this, be very careful the wrench does not come in contact with battery’s negative terminal. If you want to be extra cautious, temporarily wrap/cover battery’s negative terminal with electrical tape before doing this step.
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Connect negative cable to battery’s negative terminal. When doing this, be very careful the wrench does not come in contact with battery’s positive terminal. If you want to be extra cautious, wrap/cover battery’s positive terminal with electrical tape before doing this step.
If you short the two battery terminals with a metal tool, it can get hot so fast you can burn your hand before you even have time to let go.
And then we move on to 24 volt aircraft systems.
Burn a hole in a pressurized bulkhead on a Beech King Air. Rut Row !!!
Had just recharged an auto battery that I used on N old riding mower. It sat at my feet bungee corded to the steering post. It was just for starting, there was no working recharging system left on that old rig. It was my ‘drive into the brush until it starts to tilt up too far as a sort of mini-brush-land clearing machine.’
I just pushed the negative terminal connector onto the batter for starting & then removed. I could get many starts before needing recharging.
It was a very still day. ( I think some H had collected around the battery some how.) When I hit the starter button there must have been an itty bitty spark between the terminal & the lead connector, I have seen them before on many batteries with bad connection when a heavy load is applied, & it blew about 1/3 of the top off, about ½ the acid out & was all over me. Tiny bit got in one eye but after a quick wash down with the garden hose I was good. Clothes, I did not even try, were going to be toast real quick. Wife was not amused. ( I was very lucky. )
Person needs to not get careless around batteries of any kind or size.
It has been said many times on this thread that in Canada and The USA, that all autos are negative ground. Today, and for many decades this is and has been true. However, in the fortys, fiftys and earlier many autos were positive ground. So unless you are working on antique machinery, all is negative ground.
I once jump started a D-2 Caterpiller with my '64 VW Baja. The VW is negative ground. I jumped the six volt battery under the back seat to the Cat’s six volt battery. I did not notice that the door on my Baja was hard up against the tracks of the D-2. When I hooked the first jumper up to the Cat’s positive post and then to the VW’s positive post, it arced brightly! Since It was my first cable, I did not expect it to arc. When I investigated the cause, I realized that the Cat was positive ground. After I closed the door on the Baja, the jump start went as planned and all was well.
My late father’s 1966 MG was positive earth - my brother has it now, don’t know if he’s had it converted. He did get the electronic ignition.
I was confused when I first started reading this, then I figured out my problem - I was thinking about jumper cables rather than battery removal.
Thought in case anyone else was reading this with the same misguided perspective, I’d clarify that with the battery still hooked up to the car, the more dangerous connection is hooking the positive to a cable precisely because it’s not grounded to the car, so it’s best to connect the positive last and remove it first when attaching jumper cables.