# jumping a car and the negative battery terminals **URL:** \ **Category:** Factual Questions\ **Created:** [April 20, 2018, 5:22pm UTC](https://boards.straightdope.com/t/jumping-a-car-and-the-negative-battery-terminals/812799 "2018-04-20T17:22:16Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![am77494](https://avatars.discourse-cdn.com/v4/letter/a/d2c977/32.png) [@am77494](https://boards.straightdope.com/u/am77494)\ **Post date:** [April 21, 2018, 3:29am UTC](https://boards.straightdope.com/t/jumping-a-car-and-the-negative-battery-terminals/812799/21 "2018-04-21T03:29:26Z")
> [@Chronos](#): > > You’d expect the YouTube video to be staged-- Why else would he have had the camera running? The question isn’t whether it was staged; it’s whether the staging represents a realistic model of something that could happen in a non-staged situation. Exactly Chronos. The battery used in the demonstration is not a realistic battery compared to a sealed battery in cars. The charger used in the demonstration is not a realistic charger and the sparks are not realistic of the sparks produced in making a connection. ---
**Author:** ![am77494](https://avatars.discourse-cdn.com/v4/letter/a/d2c977/32.png) [@am77494](https://boards.straightdope.com/u/am77494)\ **Post date:** [April 21, 2018, 3:31am UTC](https://boards.straightdope.com/t/jumping-a-car-and-the-negative-battery-terminals/812799/22 "2018-04-21T03:31:08Z")
> [@HoneyBadgerDC](#): > > In every case but one they were in a group of 4 truck batteries and were overcharged and over heated due to one defective battery in the group and yes they were sealed batteries but leaking. One case was in the 1960’s, not a sealed battery, I was a kid and don’t remember anything but hooking up the cables to jump start the car and it blew. Thanks Honeybadger for the reply. I suspected the same. ---
**Author:** ![wolfpup](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/wolfpup/32/10618_2.png) [@wolfpup](https://boards.straightdope.com/u/wolfpup)\ **Post date:** [April 21, 2018, 3:36am UTC](https://boards.straightdope.com/t/jumping-a-car-and-the-negative-battery-terminals/812799/23 "2018-04-21T03:36:45Z")
> [@caligulathegod](#): > > I can’t recommend enough one of those portable jumpstart kits. Saved me a few times when I was stuck at night with no one else around to help jump my car. They have them now small enough to fit in the glovebox. I have one of those, and though I’ve never had to use it, it’s been highly rated in credible reviews so I have some confidence in it. It’s a lithium-ion pack small enough to fit in a coat pocket or keep in a glove box, and according to several reviews it can start large V8 engines multiple times between charges. But apparently there is a huge variance in quality in the different competing brands, and some of the more famous ones have fakes and lookalikes in the marketplace, so it’s important to read the reviews and shop carefully. But it’s amazing how much power can be held in a relatively small handheld Li-ion battery pack. ---
**Author:** ![am77494](https://avatars.discourse-cdn.com/v4/letter/a/d2c977/32.png) [@am77494](https://boards.straightdope.com/u/am77494)\ **Post date:** [April 21, 2018, 4:07am UTC](https://boards.straightdope.com/t/jumping-a-car-and-the-negative-battery-terminals/812799/24 "2018-04-21T04:07:16Z")
> [@wolfpup](#): > > But it’s amazing how much power can be held in a relatively small handheld Li-ion battery pack. Now that scares me. Lithium batteries and cold cranking amps are a very dangerous mix. ---
**Author:** ![Flyer](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/flyer/32/7298_2.png) [@Flyer](https://boards.straightdope.com/u/Flyer)\ **Post date:** [April 21, 2018, 5:05am UTC](https://boards.straightdope.com/t/jumping-a-car-and-the-negative-battery-terminals/812799/25 "2018-04-21T05:05:08Z")
> [@am77494](#): > > Now that scares me. Lithium batteries and cold cranking amps are a very dangerous mix. I would take the very low possibility of an exploding car battery over the possibility of an fiery, exploding lithium battery. ---
**Author:** ![Ashtura](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ashtura/32/2963_2.png) [@Ashtura](https://boards.straightdope.com/u/Ashtura)\ **Post date:** [April 21, 2018, 5:12am UTC](https://boards.straightdope.com/t/jumping-a-car-and-the-negative-battery-terminals/812799/26 "2018-04-21T05:12:33Z")
Huh. I think I’ve jump started dozens of times over the years on the negative terminals (last time a couple weeks ago) with no issues. TIL. ---
**Author:** ![duffer](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/duffer/32/1026_2.png) [@duffer](https://boards.straightdope.com/u/duffer)\ **Post date:** [April 21, 2018, 5:38am UTC](https://boards.straightdope.com/t/jumping-a-car-and-the-negative-battery-terminals/812799/27 "2018-04-21T05:38:49Z")
I’ve jumped dozens of batteries over the years. Dead Positive to Live Positive, Live Negative to Dead Negative. Started every time. I suspect the (not really) myth is based on older batteries. And don’t see how gas build-up is a hazzard since the hoods are open and have free air flow. How is the hydrogen building up? ---
**Author:** ![Capn\_Carl](https://avatars.discourse-cdn.com/v4/letter/c/838e76/32.png) [@Capn\_Carl](https://boards.straightdope.com/u/Capn_Carl)\ **Post date:** [April 21, 2018, 8:03am UTC](https://boards.straightdope.com/t/jumping-a-car-and-the-negative-battery-terminals/812799/28 "2018-04-21T08:03:53Z")
> [@duffer](#): > > I’ve jumped dozens of batteries over the years. Dead Positive to Live Positive, Live Negative to Dead Negative. Started every time. I suspect the (not really) myth is based on older batteries. And don’t see how gas build-up is a hazzard since the hoods are open and have free air flow. How is the hydrogen building up? From what I’ve read, hydrogen is building up inside the battery. ---
**Author:** ![Fridgemagnet](https://avatars.discourse-cdn.com/v4/letter/f/22d042/32.png) [@Fridgemagnet](https://boards.straightdope.com/u/Fridgemagnet)\ **Post date:** [April 21, 2018, 10:01am UTC](https://boards.straightdope.com/t/jumping-a-car-and-the-negative-battery-terminals/812799/29 "2018-04-21T10:01:01Z")
If you’re using a charger then you can avoid sparks by connecting it to the battery before plugging the charger into the mains electricity supply. This also prevents high voltage spikes that can damage the car’s various electronic systems. Some cars require that the battery is disconnected before charging, usually for this very reason. My own car recommends a disconnected battery charge, but there’s a whole complicated power-down-and-reset procedure that has to be followed for this particular model so I just safely charge it _in situ_ by always connecting and disconnecting the charger when the charger is powered down. In some cars there’s another good reason for connecting the common (invariably negative) charger lead to the chassis rather than the battery terminal - there may be a current sense module between battery negative and the chassis, and if this is bypassed during charging then bad things might happen. Mrs Fridgemagnet’s BMW Mini is like this, and the manual warns that connecting a charger lead directly to the battery negative terminal might result in a trip to the dealer to unscramble the computer. ---
**Author:** ![bluezooky](https://avatars.discourse-cdn.com/v4/letter/b/e8c25b/32.png) [@bluezooky](https://boards.straightdope.com/u/bluezooky)\ **Post date:** [April 21, 2018, 11:01am UTC](https://boards.straightdope.com/t/jumping-a-car-and-the-negative-battery-terminals/812799/30 "2018-04-21T11:01:22Z")
I’ve witnessed an older wet cell battery explode caused by reversing the cables, the gas generated “explodes” out the top of the case releasing the pressure rather than catching fire. Hooking up to the engine block avoids shorting the battery. ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [April 21, 2018, 11:24am UTC](https://boards.straightdope.com/t/jumping-a-car-and-the-negative-battery-terminals/812799/31 "2018-04-21T11:24:02Z")
> [@am77494](#): > > Exactly Chronos. The battery used in the demonstration is not a realistic battery compared to a sealed battery in cars. The charger used in the demonstration is not a realistic charger and the sparks are not realistic of the sparks produced in making a connection. maintenance-free car batteries are NOT “sealed.” they’re valve-regulated. they still can emit hydrogen and oxygen at high charging currents. you know, like when jumping a flat battery. I’ve wrenched for long enough to have seen more than one “sealed” (valve regulated) battery go pop. many times it’s an internal fault which does it, and the act of trying to jump start a failed battery will blow the top off of it and get you a face full of sulfuric acid. **you are giving incorrect and dangerous advice based on nothing more than your own ignorance. STOP IT NOW.** ---
**Author:** ![FoieGrasIsEvil](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/foiegrasisevil/32/16638_2.png) [@FoieGrasIsEvil](https://boards.straightdope.com/u/FoieGrasIsEvil)\ **Post date:** [April 21, 2018, 3:29pm UTC](https://boards.straightdope.com/t/jumping-a-car-and-the-negative-battery-terminals/812799/32 "2018-04-21T15:29:00Z")
> [@Alley\_Dweller](#): > > I’ve always had bad luck trying to connect the last cable to the body. It just never seems to work. It doesn’t have to be to the body, exactly. You can get a good ground from any unpainted metal under the hood, including nuts, bolt heads, etc. > [@caligulathegod](#): > > I can’t recommend enough one of those portable jumpstart kits. Saved me a few times when I was stuck at night with no one else around to help jump my car. They have them now small enough to fit in the glovebox. In most cases they work pretty well, but if the battery is discharged enough, a jump can often get the car started when those can’t. > [@USCDiver](#): > > Why can’t you make the last connection to the terminal on the good battery? Is that one also likely to have hydrogen buildup? Because the safest way to jump the car is to go from positive on the good battery to positive on the bad, negative on the good battery to negative ground as the last connection. That’s the recommended order. The last connection is going to spark, so you’re better off that being the ground than a battery terminal on the good battery. ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [April 21, 2018, 4:04pm UTC](https://boards.straightdope.com/t/jumping-a-car-and-the-negative-battery-terminals/812799/33 "2018-04-21T16:04:51Z")
> [@Alley\_Dweller](#): > > I’ve always had bad luck trying to connect the last cable to the body. It just never seems to work. you can use any bare metal underhood. the engine is tied to the chassis with multiple ground straps, so you can clamp on to such things as the accessory front cover, alternator case, what have you. A lot of modern cars even provide a grounding lug at the ground strap attachment point to the body as a safe place to make the final connection. ---
**Author:** ![FoieGrasIsEvil](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/foiegrasisevil/32/16638_2.png) [@FoieGrasIsEvil](https://boards.straightdope.com/u/FoieGrasIsEvil)\ **Post date:** [April 21, 2018, 5:19pm UTC](https://boards.straightdope.com/t/jumping-a-car-and-the-negative-battery-terminals/812799/34 "2018-04-21T17:19:56Z")
> [@jz78817](#): > > you can use any bare metal underhood. the engine is tied to the chassis with multiple ground straps, so you can clamp on to such things as the accessory front cover, alternator case, what have you. A lot of modern cars even provide a grounding lug at the ground strap attachment point to the body as a safe place to make the final connection. I remember the first auto dealer I worked for sold Buick/GMC and I was constantly amazed by the number of (especially the Buicks) vehicles that were brand new but had sat long enough that the passive electronics (WAG) had drained the battery to the point where they would not start. The Enclaves and Lacrosses were the worst for this. This isn’t to mention other issues, like flat spots on tires, etc. Anyway, we had to use a jumpbox on these and it often wouldn’t work so we’d pull around a running car and try to jump it. Often in the very cold conditions getting a good ground seemed impossible, and the best seemed to be anyplace where the alligator clamps would stay clamped onto the engine block. Ever heard of that before? I could never tell if it was the cold or some other factor. Sometimes the cars were so dead that service had to come out and put a new battery…into a new car! ---
**Author:** ![california\_jobcase](https://avatars.discourse-cdn.com/v4/letter/c/9d8465/32.png) [@california\_jobcase](https://boards.straightdope.com/u/california_jobcase)\ **Post date:** [April 21, 2018, 5:48pm UTC](https://boards.straightdope.com/t/jumping-a-car-and-the-negative-battery-terminals/812799/35 "2018-04-21T17:48:20Z")
I know of one occasion when a jumped battery exploded. It was definitely one of the non-sealed types, which are still readily available. The electrolyte missed his face, but ate up his jeans jacket. If one \*\*\*has \*\*\*to attach the last connection at a battery terminal, it is a really good idea to first remove the caps and ventilate the battery really well by fanning the holes with a paper fan thingy such as a magazine. If the hydrogen’s there, you’ll blow it away so no explosion will occur. Replace the caps (after topping up the level if need be) before connecting. ---
**Author:** ![TSBG](https://avatars.discourse-cdn.com/v4/letter/t/77aa72/32.png) [@TSBG](https://boards.straightdope.com/u/TSBG)\ **Post date:** [April 22, 2018, 6:05am UTC](https://boards.straightdope.com/t/jumping-a-car-and-the-negative-battery-terminals/812799/36 "2018-04-22T06:05:52Z")
I have a lot less experience than many here, but I have jumped dead batteries in my life–say 10 times or so. I always follow the “regulation” order (which I always have to look up) and make the last connection to a metal part of the car away from the battery. However, I’ve never seen a spark from this last connection. Last time I did this was a couple years ago. Have I just missed the spark ever time? Or is the last-connection step more of a precaution against a _possible_ spark? ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [April 22, 2018, 1:03pm UTC](https://boards.straightdope.com/t/jumping-a-car-and-the-negative-battery-terminals/812799/37 "2018-04-22T13:03:10Z")
> [@TSBG](#): > > I have a lot less experience than many here, but I have jumped dead batteries in my life–say 10 times or so. Jumping a dead battery will often work, but it’s also bad on the alternator. If the battery is completely discharged, it’s best to put it on an external charger if possible. > [@TSBG](#): > > However, I’ve never seen a spark from this last connection. There’s usually a spark, but the intensity of the spark depends on a lot of variables. ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [April 22, 2018, 1:21pm UTC](https://boards.straightdope.com/t/jumping-a-car-and-the-negative-battery-terminals/812799/38 "2018-04-22T13:21:22Z")
Many people take precautions to not cause a spark near the battery when they’re jumping it (by making the last connection a chassis connection), and I am a proponent of this. But they don’t give a second thought to the spark that’s created at the battery terminal when they’re removing an old battery or installing a new battery. Why is that? And how many batteries have exploded when being removed from a car or installed in a car due to this spark? I am not saying sparking near a battery is not a problem. But if we are going to tell people to make the last connection a chassis connection when jumping a battery (which again, I am a proponent of), we should also tell people to wear safety googles or a safety visor when replacing a car battery. ---
**Author:** ![GusNSpot](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gusnspot/32/436_2.png) [@GusNSpot](https://boards.straightdope.com/u/GusNSpot)\ **Post date:** [April 22, 2018, 6:45pm UTC](https://boards.straightdope.com/t/jumping-a-car-and-the-negative-battery-terminals/812799/39 "2018-04-22T18:45:06Z")
About 8-10 years ago I was using an old riding mower that I would need to charge if it sat for over a week. It was an old one that had vented caps. I had had it on a charger for several hours and then tried to start it with a push button switch I had added. ( Yeah, using old parts because I was/am too poor to buy a good used one. ) When I hit the button, BOOM!!! right under the seat with the battery exposed to the front. Parts & acid all over my legs. Scared 2.5 years off my life span I think. Never had any problem with today’s sealed batteries. Been messing with airplanes all my life and I have had several 24V systems make an expensive mess. Worst one as on a Beech King Air that had the old original ni-cad batteries. A few in the military but like kills, they don’t count because… military… ---
**Author:** ![Gbro](https://avatars.discourse-cdn.com/v4/letter/g/c6cbf5/32.png) [@Gbro](https://boards.straightdope.com/u/Gbro)\ **Post date:** [April 22, 2018, 7:21pm UTC](https://boards.straightdope.com/t/jumping-a-car-and-the-negative-battery-terminals/812799/40 "2018-04-22T19:21:25Z")
> [@am77494](#): > > Exactly Chronos. The battery used in the demonstration is not a realistic battery compared to a sealed battery in cars. The charger used in the demonstration is not a realistic charger and the sparks are not realistic of the sparks produced in making a connection. You are Absolutely correct when you stated that the sparks are not realistic of the sparks produced in making a connection!! That is because the sparks in the video coming from the grinding wheel are a fraction of an electrical spark that will melt the tip off your screwdriver in a nano-second!: White hot is 1200 C as the fragments of steel being torn away and oxidized , yellow hot is 1000, red hot 650 C witch is closer to the temp of the sparks when they reach the battery that is off gassing. I would place a wager on that this battery is being reconditioned thereby off gassing much more than a normal in the reverse charging mode but that certainly doesn’t prove that off gassing isn’t common. When working on large battery banks all cell caps are removed and then a flame commonly a propane torch is used to flame off any hydrogen gas that could result in an explosion if trapped in a closed cell. And sealed battery’s are vented and hydrogen gas will escape [Previous page](https://boards.straightdope.com/t/jumping-a-car-and-the-negative-battery-terminals/812799.md?page=1) [Next page](https://boards.straightdope.com/t/jumping-a-car-and-the-negative-battery-terminals/812799.md?page=3)