How do car batteries work?

Marshall Brain

You asked:

How do car batteries work? --- Ike, Charlotte, N.C.

Marshall Brain answered:

A car battery is based on lead-acid battery technology. This technology has been around for decades, it is relatively inexpensive, it is reliable even in the harsh environment of a car (big temperature swings, lots of vibration, etc.), and a car battery will typically last three or four years before wearing out. Overall, that's a great set of characteristics compared to other battery technologies.

The article How Batteries Work offers this description of the chemical reaction that takes place in a car battery:

For example, here's what happens in one cell of a car's lead-acid battery: - The cell has one plate made of lead and another plate made of lead dioxide, with a strong sulfuric acid electrolyte in which the plates are immersed. - Lead combines with SO4 (sulfate) to create PbSO4 (lead sulfate), plus one electron. - Lead dioxide, hydrogen ions and SO4 ions, plus electrons from the lead plate, create PbSO4 and water on the lead dioxide plate. - As the battery discharges, both plates build up PbSO4 and water builds up in the acid. The characteristic voltage is about 2 volts per cell, so by combining six cells you get a 12-volt battery. A lead-acid battery has a nice feature -- the reaction is completely reversible. If you apply current to the battery at the right voltage, lead and lead dioxide form again on the plates so you can reuse the battery over and over.

Here's how lead-acid batteries are made, along with a look inside a lead-acid battery:

What happens to all the car batteries after they wear out? It turns out that, because of the unique properties of lead, they are relatively easy to recycle, as shown here: