Friday, September 22, 2023


RVelectricity – 12-volt battery dangers (Warning: graphic content)

By Mike Sokol

Dear Readers,
I see more and more of you changing batteries in your RV. Perhaps you’re adding a second battery for more boondocking capacity, upgrading to Lithium chemistry, or simply replacing worn out batteries that no longer hold a charge. In any event, there are a lot of untrained consumers handling RV batteries without proper safety precautions.


Is 12 volts DC dangerous?

You bet your sweet bippy it is, but probably not for the reasons you’re thinking about. While 12-volt batteries have too low of an electrical potential to cause a dangerous electric shock like a hot-skin contact voltage, this class of batteries has the capability of supplying hundreds or even thousands of amperes of current if a metallic conductor makes contact between the plus and minus poles. And while the human body offers too high of a resistance to allow significant amperage to flow, any metal jewelry you’re wearing offers a low-resistance path that will heat up cherry red in seconds, right after it welds itself in place.

How hot can it get?

Well, if you’re unlucky enough to have your finger or hand trapped by a piece of jewelry that’s rapidly heating up due to making contact and welding itself between the battery and vehicle frame, then this chart shows you just what temperature your metal ring, watch band or bracelet achieved.

Note that if you can begin to see it glow cherry red, it’s already made it to 1,400 degrees F. And if it gets up to yellow, then you’re touching metal that’s approaching 2,000 degrees Fahrenheit.

This is a high enough temperature to cause 3rd degree burns in seconds, then quickly begin tendon and bone damage. Yes, it’s possible to lose a finger or even a hand if you can’t break your jewelry free from the welded connection fast enough.

A real-world example

Here’s what happened to one of my RVelectricity Facebook members last week that should serve as a warning to all of us. Even though he was a 25-year certified ASE mechanic and said he should have known better, he admitted to getting complacent while working around an alternator. Note that he was wearing a thin metal bracelet made from a stainless steel bicycle spoke, which you can see in the top right part of the picture.

Somehow he accidentally made contact between the main wire on the alternator and something metal in the engine compartment of his RV. Virtually every piece of metal in an RV is bonded to the frame, and the negative terminal of the batteries are also bonded to the vehicle frame. Because the alternator is connected directly to the battery via this primary wire, the current can flow either way. That allowed the full cold cranking amps of the batteries to be available to heat up that thin metal bracelet after welding itself in place.

No, it’s not a shock, it’s a burn…

While it’s true that you really can’t get shocked from a 12-volt battery (unless you can put your tongue across it, and even then it’s probably not dangerous), anything metal connecting the positive and negative battery terminals will cause hundreds of amperes of current to flow and heating to occur.

I’m sure the temperature of the bracelet reached way over 1,000 degrees F in an instant, and he tried to get it loose quickly. But since the bracelet had tack-welded itself between the alternator terminal and vehicle frame, all he could do was attempt to pull the red hot metal loose using his bare flesh. Here’s what the top of his arm looked like.

It gets worse, much worse…

You can see from the burn marks on the bottom of his arm that he had to pull on the red-hot bracelet multiple times in an attempt to free that thin piece of wire from the huge current flowing through it (probably upwards of 1,000 amperes), with the temperature continuing to rise. Stainless steel melts at around 2,700 degrees Fahrenheit, and with enough time an RV battery can probably get it up to that temperature.

Every time he tried to pulled away from it, the metal bracelet burned into his flesh even deeper. He must have been in incredible pain for the time it took to free himself from the red-hot metal bracelet. This picture shows you just how much damage a bracelet heated up by an RV battery can cause.

But he’s lucky…

This type of burn injury can not only be extremely painful, there are other hidden dangers if you short out your RV or vehicle battery. For example, it’s also possible to cause acid to boil out of a flooded-cell battery and hit you in the eye (I witnessed this happen to my dad many years ago when he got the jumper cables reversed).

If that’s not bad enough, you can even cause a lead-acid battery to explode sending sulfuric acid everywhere (I witnessed this at the gas station I worked at during high school). And you can also lose the use of a finger or your hand. Read more on this below.

Wedding rings are dangerous too

I personally witnessed a car mechanic get his wedding ring trapped between a wrench on the positive terminal of a vehicle battery and the car frame, welding itself into place.

I heard him screaming while he was trying to break free of the red-hot ring, and then saw him run to the sink in the back of the shop to submerge his hand in cold water. I could see a cloud of steam rising from the sink, attesting to just how hot the ring got.

The paramedics who transported him to the emergency room said he was lucky he didn’t lose the finger. But he did have tendon damage and never regained full use of his finger.

What can you do to stay safe?

  • Remove all jewelry including rings, bracelets, watches and necklaces when working around any live electrical circuits, especially batteries. Just remember that RV and vehicle batteries are ALWAYS live. Anything metal can cause a short circuit with very bad results.
  • Wear safety glasses when working around anything electrical. I have pictures of exploding bits of metal flying from copper wire during a short circuit that could easily put our your eye. Safety glasses are a must.
  • Disconnect the negative terminal of the battery first, and put it back on last. That way if your wrench accidentally makes contact with the vehicle frame, because it’s on the negative terminal of the battery there’s no voltage differential to drive the current. Once the negative terminal of the battery is removed, it’s then safe to disconnect the positive terminal. At that point, even if your wrench makes contact with the frame the battery is isolated from the chassis ground and no current can flow.

Learn more at the FROG Virtual Rally – Sept. 30 to Oct. 4, 2020

If you’re a member of FROG (the Forest River Owners’ Group), I’ll be teaching several RVelectricity virtual seminars during the TechnoRV FROG Virtual Rally from September 30 through October 4. I’ll be presenting a virtual JAM Session (Just Ask Mike) about 12-volt battery safety, including safe ways to use jumper cables, how to avoid creating sparks that can cause a hydrogen-oxygen battery explosion, etc.

If you’re not already a member of the Forest River Owners’ Group and own a Forest River RV, you can sign up for free to become a member of FROG HERE.

This is a FROG members only rally

For more information on how you can attend this virtual rally along with lots of other seminars including the JAM Sessions that “yours truly” will be teaching online beginning September 30, please sign up for the TechnoRV FROG Virtual Rally HERE.

But if you’re not a FROG member don’t worry about missing out on these videos, as I’ll repost them the week after the rally on my own RVelectricity Youtube channel. So stay tuned.

Please be careful around 12-volt batteries. And let’s play safe out there….

Mike Sokol is an electrical and professional sound expert with 50+ years in the industry. His excellent book RV Electrical Safety is available at For more info on Mike’s qualifications as an electrical expert, click here.

For information on how to support RVelectricity and No~Shock~Zone articles, seminars and videos, please click the I Like Mike Campaign.



  1. Regarding removing power. If the RV is “positive to Frame”, disconnect the positive side first if you do not have a disconnect switch installed.

  2. I was taught to wrap the metallic handles and shafts of wrenches and screwdrivers with shrink wrap tubing or heavy layers of electrical tape so that it’s almost impossible to cause a short.

    • on screwdrivers, wrap all the metal other than about 3/8″ of the blade
    • on wrenches wrap as close to the opening as feasible and then wrap the entire rest of the wrench. That means picking one end of a combination open-end closed-end wrench and completly covering up the other end.

    For socket wrenches, Harbor freight has inexpensive composite-plastic ratchets. Wrap the outside of sockets you may use near batteries. If you use an extension, wrap it.

    The wrap hardly ever gets in the way.

  3. I know that this is a 12 volt DC topic, but this is what I was taught.
    I am a retired union commercial/industrial electrician, and in our apprenticeship classes it was drilled into us to “Never wear any Jewelry on your hands/wrists”.
    Not only for shock hazard ,but with crush hazard for your fingers.
    My wedding ring was a stud earing, and my wristwatch was hung on a belt loop.
    47 years later, same scenario.
    Work Safe!

    • When I had my first real job back in the mid-70’s I eventually became the plant safety engineer in charge of keeping our shop electricians safe while working on industrial power. So I was trained by the then new OSHA on all the ways you can get injured or killed while working around electricity. Yep, I got to see all the autopsy photos of electricians who didn’t pay attention to what they were doing. Work Safe was one of our mottos.

  4. Just did a battery cleaning service on my 8-6V battery bank. All master switches were off. I wore rubber gloves, no jewelry and had taken very serious precautions on making sure I did not hurt myself or the rv. 12VDC can kill you if the circumstances are set correctly, so all be careful. I did not disconnect them from the coach, as their is a specific order to disconnect because of the inverter, and I don’t want to burn that up. I use NO-OX-ID-Special A preservative grease to keep the terminals from corrosion. Annual cleaning is necessary. When they need to be replaced, AGM”s are the most cost effective option unless Lifpo4 prices come down by at least 50-60%. I had a friend who was trying to get the battery cap off and was using screwdriver, he arced across terminals, and had an explosion in his face, fortunately he had on glasses, and was not injured, but we heard it and it scared us to next week. He knew better, but for that one second he forgot, and almost got hurt.

    • Watch the price on Lithium tumbling. Right now, 105ah LionEnergy is about 650 at Costco. Over a thousand last year. Remember when a 40 inch flat screen tv was 1500 bucks? Now under 200 with much better spec’s. Mass production, it’s a wonderful thing. Only way AGM’s will survive is if they can lower their prices.

  5. Thank you for all wonderful information you provide Mike !!! Just wanted to put in my two cents I worked professionally as an air craft ,motor cycle, and auto -truck tech so most of my experience is of dc voltage some machines are positive ground so attention must be paid to removing the proper cable regardless of which is removed I always wrapped it up in a towel then remove the other cable the battery or batteries were covered. If major surgery was required the battery was removed from the machine as I paid a lot for the chrome on my tools

  6. We had a mechanic get careless and lay a tool tray across the terminals. The top blew off and he was rushed to the ER to get his eyes washed out. When he got back he now had to install a new battery. He picked up the old one but acid is slippery and it dropped to the floor, like dropping a bucket of water the acid splashed straight back up into his eyes. Back to the ER 🙁 Another mechanic finished the job!

    • Yeah, I had something similar happen in the truck repair shop where I worked cleaning out oil pans and changing tires on semi-trucks for a summer job as a 16 year old kid. Flooded cell batteries are surprisingly easy to blow up.

  7. Many diesels have 24 volt starter systems. If you have to jump start one of these, be doubly sure about how they will be connected. If is common for a battery to “blow its’ lid” if not hooked up right. The possible acid spray is beyond dangerous.

  8. Back in 1971 I welded myself to the under-dash add-on amp gauge on my ’65 Mustang. I don’t recall taking the time to stick my head under the dash to judge the color temp of my wedding ring before jerking my hand away from the gauge. Lesson learned though. As a off and on auto mechanic until 1980 I always removed all watches and jewelry before leaving home.

    • Yes, I’m pretty sure that most people who heat up a bracelet or ring on a battery don’t take the time to observe the color/temp, but a few say that it was glowing. Ouch!

  9. Whether using a socket or a wrench or any other metal tool near energized circuits I always apply a layer or two of electrical tape or masking tape (because it leaves less residue) to insulate the non-contact parts of the tool, just in case…

  10. Lifetime mechanic here, just retired. Seen other guys get hurt this way, haven’t worn jewelry since my 20’s. Just got a ring as a retirement gift from my employer. I’ll be taking it off if/when wrenching as I want to keep it nice anyway. As you might guess, the wedding ring is in great shape…

  11. The burned wrist looks just like mine about 1975. My metal watch band crossed ampmeter terminals behind the dash of a large truck. Never did wear a watch after that!

  12. Mike; I’ve heard (anecdotally) that on RVs equipped with Magnum Energy inverters that one should always disconnect the positive terminal first, and reattach it last when servicing the house batteries.

    As a former Navy electrician this makes no sense to me. I’ve always taken off the (-) first and put it on last.

    Do you have any information on this Magnum quirk, or if this is just an old wive’s tale?

  13. I was changing the battery on a car once, using a combination wrench. I had work gloves on because I didn’t want to get my hands dirty. I accidentally dropped the wrench and it made contact between the battery terminals. It instantly made a spark and whatever grease was on the terminals flared. I quickly grabbed the wrench and found that it was so hot that I could feel the heat even with gloves. Luckily it was not stuck in place. There were “spot weld” marks on the wrench where the contact was made. Needless to say I have a lot more respect for car batteries than I did before, and gloves and eye protection are required and not optional.

    • I witnessed a similar incident at vocational school when a young man dropped a wrench on a battery of a running dump truck. Since the battery was charging and giving off hydrogen gas the spark from the wrench caused the battery to explode ! Fortunately the young man was wearing safety glasses and after much flushing his eyes and face with water he was ok.

  14. In 1965, I was in an radio unit that had very high output transmitters. The radio maintenance sgt. accidently got his ring finger between a high output power supply. Removed the finger very nicely. Medics could not do anything except a bandage.
    I never wear anything metal that may cause any contact.


Please enter your comment!
Please enter your name here

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Sign up for the

RVtravel Newsletter

Sign up and receive 3 FREE RV Checklists: Set-Up, Take-Down and Packing List.