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The Importance of Car Batteries: What’s Inside a Motor Vehicle Battery?

A motor vehicle battery has two jobs: running the onboard electronics and cranking the engine. If you’re adding power-hungry accessories, an uprated unit is recommended.

Traditional lead-acid batteries have rows of cells filled with battery acid and topped with heavy terminals that correspond to positive and negative plates. They have to be topped up with distilled water periodically to avoid overheating and possible fires.

Charger

Battery chargers vary in amperage output, and it’s important to find one that matches the amount of power you need. On the low end, most chargers are one to three amps for a trickle charge, while higher output models provide up to twelve amps.

During operation, a car battery creates electricity by combining lead dioxide and pure lead plates within its cells. The resulting chemical reaction transfers positive lithium ions between the cathode and anode. The movement of these ions generates electric current that powers your car’s electrical systems and ignition system.

When selecting a battery for your vehicle, make sure it has the correct BCI (Battery Council International) group code. This determines the battery’s dimensions, terminal type, mounting system, polarity and cold cranking amps (CCA). A battery with an incorrect group size won’t fit your vehicle. Check the date sticker on your battery or its manufacturer’s website for a group code.

Voltage Regulator

A voltage regulator is used to regulate the output of the alternator. It monitors battery charge to prevent overcharging or undercharging, compensates for temperature variations, and detects faults.

A bad voltage regulator can lead to the battery warning light or check engine light turning on due to the charging system not operating correctly. Other symptoms can include headlights that appear dimmer than usual and other electrical components that act erratically.

In many newer vehicles, the voltage regulator has been replaced by a computer that controls the alternator output directly. In this type of setup, the PCM monitors battery current and sends a signal to change the on-time for current flow through the alternator field coil. It can do this by connecting to a voltage regulator controller through a dedicated battery wire or using an in-vehicle data network that connects the PCM, body control module (BCM), and other modules. Older systems use an external voltage regulator like this one with a BATT terminal hooked directly to the battery.

Battery Cells

The battery cells store the energy that powers your car. Each voltaic cell consists of two electrodes (for the lead-acid cells used in cars, Pb and PbO2) separated by an electrolyte (for these batteries, a 35% solution of sulfuric acid, H2SO4, in water). Chemical reactions at each electrode provide the battery’s emf. At full charge, the ions of both the electrodes and the electrolyte are highly concentrated near the electrodes. After driving for a few minutes, you deplete the ions at the electrodes and they spread throughout the bulk of the electrolyte. With the ion density now low, the battery can’t start your car.

Traditionally, lead-acid car batteries consisted of six galvanic cells in a series circuit. Each cell provided 2.1 volts at full charge. The cells are joined together by short heavy straps from the positive plates of one cell to the negative plates of another. The plates are separated by plastic separator bags, which allow the electrolyte and ions to pass but prevent the plates from contacting each other and short-circuiting.

Maintenance

The reliability of an car batteries depends on the care it receives. Driving it regularly helps, as does using a trickle charger during periods of inactivity. It’s also important to avoid parasitic drains, caused by components like butchered wiring looms or dodgy aftermarket stereos that keep drawing energy from the battery even when the car is parked.

The best way to prevent these problems is to keep the battery charged, and a quality voltage maintainer (also known as a battery tender) can help do this. It’s a good idea to inspect the battery on a regular basis, and clean the terminals with a 1:1 mixture of water and baking soda. It’s important to disconnect the negative terminal first when removing a battery, and to use a wrench instead of a screwdriver, as touching the ground can cause a short circuit. It’s also a good idea to make sure the battery is secure, as vibration can eventually kill many flooded plate batteries.