How does a lead acid battery work

You probably don’t give them much thought, but lead acid batteries are everywhere—from starting your car to powering golf carts. They’re reliable, affordable, and have been around forever. But have you ever wondered how they actually store and release all that power? Let’s take a look under the hood.

At its core, a lead acid battery is a simple chemical power plant. It’s made up of three key components: a positive plate, a negative plate, and an electrolyte. The positive plate is made of lead dioxide, a dark brown, powdery substance. The negative plate is pure, spongy lead. And the electrolyte? That’s just a mixture of sulfuric acid and water.

When Your Battery is Discharging

When you turn on your car’s headlights or start the engine, a chemical reaction kicks off. The sulfuric acid in the electrolyte starts reacting with both the lead dioxide on the positive plate and the spongy lead on the negative plate. This reaction converts both materials into lead sulfate, and in the process, it releases electrons. Those electrons flow from the negative plate, through your car’s electrical system, and back to the positive plate. That continuous flow of electrons is what we call electricity, and it’s what powers everything. As the battery discharges, the sulfuric acid gets used up, and the electrolyte becomes mostly water. That’s why a “dead” battery has a lower specific gravity—it’s less dense because it has more water and less acid.

When Your Battery is Charging

So, what happens when your car’s alternator (or a battery charger) starts doing its job? It reverses the entire process. By applying an external voltage, the charger forces the electrons back into the battery, effectively reversing the chemical reaction. The lead sulfate on both plates is converted back into its original forms: lead dioxide on the positive plate and pure lead on the negative plate. At the same time, the sulfuric acid is replenished, and the electrolyte becomes more concentrated again. This is why you can recharge and reuse these batteries over and over again. It’s a beautifully simple, reversible chemical reaction.

A Few Things to Keep in Mind

While this process is straightforward, a few things can go wrong. If you let a lead acid battery sit for too long in a discharged state, the lead sulfate crystals can harden and become difficult or impossible to convert back. This is known as sulfation and it’s a leading cause of battery failure. Also, these batteries aren’t fans of being completely drained—doing so repeatedly shortens their lifespan. That’s why it’s best to keep your car’s battery topped up, and to avoid leaving your lights on all night! Understanding how these batteries work helps you take better care of them, keeping your car running smoothly for years to come.