While there are certain aspects of automotive electrical systems that are dangerous and batteries themselves can also be dangerous, your car battery can’t actually electrocute you. In fact, under normal conditions, a 12-volt car battery will usually not even shock you.
For sure anyone who watched a lot of spy dramas or thrillers will wonder what we are saying, as the scene with a captured hero, restrained and helpless to resist while his captor hooks up a pair of jumper cables to a car battery is so familiar! As dutiful consumers of media, we’ve been conditioned to know that means our hero is about to be tortured, possibly to within an inch of his life. But let’s see why this is just another one of the tricks Hollywood uses for offering a more engaging story and a bigger spectacle, as a car battery actually can’t electrocute you.
The math can get a little complicated, but the main reason that you can safely touch the positive and negative terminals of a typical car battery, and walk away unscathed, has to do with the voltage of the battery. Traditional car batteries are capable of delivering a lot of amperage in short bursts, which is the main reason that ancient lead acid technology is still in use. Starter motors require a lot of amperage to run, and lead acid batteries are good at providing short, intense bursts of amperage. However, there’s a world of difference between the coils of a starter motor and the high contact resistance of the human body.
Simply put, voltage can be thought of as “pressure,” and the 12 volts of a car battery simply don’t provide enough pressure to push any significant amount of amperage through the contact resistance of your skin.
That’s why you can touch both terminals of a car battery without receiving a shock, although you may feel a tingle if your hands are wet. Certainly nothing like the confession-inducing, potentially-deadly, electrical torture you may have seen in the movies or on television, though.
Be careful though, as not all car batteries are 12V. There was a huge push in the early 2000 s to move from 12V systems to 42V systems, which would have been much more dangerous to work with, but the switch never really materialized for a variety of reasons.
However, hybrid and electric vehicles often come with two batteries: a traditional lead acid battery for starter, lighting and ignition (SLI) functions, and a much higher voltage battery or battery pack to run the electric motor or motors. These batteries often use lithium-ion or nickel metal hydride technology instead of lead acid, and they are often rated at 200 or more volts.
The good news is that hybrid and electric vehicles typically don’t keep their high voltage battery packs anywhere that you’re likely to run into them on accident, and they almost always use some type of color code to warn you about high voltage wires. In most cases, high voltage wires are color coded orange, although some use blue instead, so it’s a good idea to verify what color your vehicle uses before you try to work on it.
12-Volt Car batteries are not harmless, though. There are many ways you can be injured by car batteries:
The main danger associated with car batteries is explosion, which can occur due to a phenomenon known as “gassing,” where the battery releases flammable hydrogen gas. If the hydrogen gas is ignited by a spark, the entire battery can explode, showering you with sulfuric acid. This is why it’s so important to follow the correct procedure when hooking up jumper cables or a battery charger.
Another danger associated with car batteries has to do with accidentally bridging the terminals, or accidentally bridging any +B wire or connector, like the starter solenoid, to ground. While a car battery can’t pump a dangerous amount of amperage into your body, a metal wrench has far less resistance, and will tend to grow extremely hot, and may even become welded in place, if it bridges battery positive to ground. That’s pretty much bad news all around.
Keep in mind that, although you can’t be electrocuted by simply touching the terminals of a regular car battery, due to the low voltage, you can receive a nasty shock from other components of a traditional automotive electrical system. For instance, in ignition systems that use a cap and rotor, an ignition coil is used to provide the tremendous amount of voltage that’s required to push a spark across the air gap of a spark plug. If you run afoul of that voltage, typically by touching a spark plug wire or coil wire with frayed insulation, while also touching ground, you will definitely feel a bite.
Source: lifewire.com (Jeremy Laukkonen)