Automotive batteries come in many shapes and sizes, but their operating principles are remarkably similar. In this Tech Center installment, we'll look at the basic automotive battery. Then we'll close by discussing ways to maintain your battery to ensure a long life.

The modern automotive battery is a lead-acid storage design. In short, it's an electrochemical device that converts chemical energy into electrical energy. When the battery is placed under a load, such as when the ignition is switched on, the device converts stored chemicals into electricity, and the current flows through the wires to its destination.

A standard 12-volt, lead-acid battery is made up of six cells connected in series. Each cell produces approximately two volts.

The cells are filled with an electrolyte. An electrolyte is an ionized bath — in this case, sulfuric acid (H2SO4) diluted with water — that generates an electrical current when called upon.

Each cell also contains plates (grids of active material), which are both positive and negative. Typically, the positive plates contain lead dioxide (PbO2), while the negative plates are composed of straight lead (Pb).

The plates are formed into a plate group, which holds a number of plates of the same polarity (for instance, all positive or all negative). The like-charged plates are welded to a post strap. The plate groups are then alternated within the battery — positive, negative, positive, negative. There is usually one extra set of negative plates to balance the charge. To ensure that the different plate groups don't touch each other, non-conductive sheets called separators are inserted between them.

The battery case, which holds all these components, is made from molded polypropylene.

A maintenance-free battery, similar in design to a conventional automotive battery, is really just a heavier-duty version of the same arrangement. Many of the components have thicker construction, and different, more durable materials are typically used. For example, the plate grids often contain calcium, cadmium or strontium, to reduce gassing (which causes water loss) and self-discharge. This design is called a lead-calcium battery. The heavier-duty parts ensure that fluid loss is kept to a minimum and that components have a much longer life, making it a closed system.