Your vehicle’s battery is basically an electrical fuel tank, and your alternator is the electrical “pump” that refills it. Over time, batteries lose their cold cranking amps until they get too weak and must be replaced.
While most drivers are used to seeing the battery’s casing, have you ever wondered, “What is the acid in car batteries?” In this article, we’ll take a look at the complex, polar liquid that helps run your vehicle’s essential electric systems.
Caution: Never work around any car battery without eye protection.
Your car’s battery typically consists of an outer shell or case, a set of terminals, and negative and positive battery plates separated by a battery separator. In most batteries, the battery acid consists of a sulfuric acid and water solution. Battery acid serves as an electrolyte.
To put it very simply, when all the electrons are stored on one side of the plates in the battery, they want to go to the other side and will take any path they can find. When they all move to where they want to be, the battery can do no more work until they’re “pumped” back to the other side of the plates.
For the most part, gas-powered vehicles rely on lead-acid batteries. Car batteries are each made up of six smaller batteries lined up in a series. These smaller batteries contain battery acid made up of 30-50% sulfuric acid. Inside the acid sit two plates, one that’s negatively charged (anode) and one that’s positively charged (cathode). A battery separator keeps the two plates apart.
Thanks to the separator, each plate has its own chamber, and the acid in one chamber can’t mix with the acid in the other chamber. This prevents the electrons that the battery acid and plates produce from flowing between the plates through the battery acid. The electrons instead flow through the vehicle’s electric systems, powering them as they flow.
As the vehicle draws power, electrons move through the electric system from the battery’s anode to its cathode. The alternator moves these electrons back to the anode, creating a stable cycle of moving electrons as the vehicle runs. But how do acid and two metal plates create electricity? It’s all thanks to a series of chemical reactions.
Lead dioxide (PbO2) makes up the cathode while a lead (Pb) sponge makes up the anode. Both plates react to the sulfuric acid (H2SO4) by creating lead sulfate (PbSO4). For chemistry enthusiasts, this is what the reactions look like:
PbO2 + 4H+ + SO4— + 2e- → PbSO4 + 2H2O and Pb + SO4— → PbSO4 + 2e-
The cathode uses up two electrons as it reacts with the sulfuric battery acid to create the lead sulfate, while the anode produces two electrons in its process. The alternator reverses the process to recharge the battery, transforming the lead sulfate back into lead dioxide and lead.
There’s no acid in a fully discharged lead-acid battery. Instead, the sulfuric acid will turn both plates into lead sulfate, and the acid between them will turn into water.
Battery acid has the following properties:
Apart from lead-acid car batteries, there are also lithium-ion (Li-ion) car batteries and solid-state car batteries. Li-ion batteries are common in electric vehicles (EVs), and they use lithium salt instead of sulfuric acid as their electrolytes. Meanwhile, some modern EVs have solid-state batteries that don’t use liquid electrolytes at all.
Lead-acid batteries are safe to use in your vehicle provided the batteries are still in good shape. A leaking or otherwise damaged battery is another story. Battery acid can be dangerous in certain situations.
Battery acid can negatively affect your health and safety if you don’t handle it properly. Sulfuric acid is highly corrosive and can burn you if it touches your skin. If you notice your battery leaking acid, it’s best to ask a professional to remove and replace it.
If your vehicle’s lead-acid battery cell becomes inoperative, it might start releasing alarming levels of hydrogen while charging. This is especially dangerous if the battery’s overheating or overcharging. While hydrogen isn’t toxic, it’s highly explosive when there’s a lot of it in one area.
Now that you know what acid is in car batteries, you should be able to take proper precautions when handling a damaged or inoperative battery. It’s a complex and interesting device that continues to power many vehicles to this day, but you definitely don’t want any battery acid getting on your skin.
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