Automotive battery facts for kids
An automotive battery or car battery is a special kind of rechargeable battery that helps start a motor vehicle. Its main job is to send a strong burst of electricity to the starter motor. This motor then gets the car's main engine (which uses gasoline or diesel) running. Once the engine is on, the car's electrical parts, like the radio and lights, still get power. The alternator then recharges the battery as you drive.
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How Car Batteries Work in Modern Cars
For Gasoline and Diesel Engines
When you start a car, the battery only uses a tiny bit of its power, usually less than three percent. Because of this, car batteries are made to give a lot of power very quickly for a short time. They are often called "SLI batteries," which stands for Starting, Lighting, and Ignition.
SLI batteries are not meant to be completely drained of power. If they lose all their charge, it can shorten their life. Besides starting the engine, an SLI battery also provides extra power when the car's electrical needs are more than what the charging system can give. It also helps keep the electricity flow steady, preventing harmful power surges.
While the engine is running, most of the power comes from the alternator. This part has a voltage regulator that keeps the power steady, usually between 13.5 and 14.5 volts. Most modern SLI batteries are lead-acid type. They have six connected parts (called cells) that give a total of 12 volts for most cars and light trucks. Bigger vehicles, like heavy trucks, might use 24-volt systems.
Safety Tips for Batteries
Sometimes, hydrogen gas can build up around the negative part of the battery, especially if the battery vents are blocked or the area isn't well-aired. If there's a spark nearby, this gas can explode. This can happen when starting the engine, often if the battery parts are rusty or dirty.
A study in 1993 found that many battery explosion injuries happened while people were charging the battery. Other times were when connecting cables or jump-starting a car. It's important to connect jumper cables correctly: always connect to the dead battery first, then to the charging source, and connect the negative cable to the car's metal frame, not directly to the negative battery post. Most injuries from these incidents involved chemical burns or eye injuries. Always be careful and follow safety instructions when working with car batteries.
For Electric and Hybrid Cars
Electric vehicles (EVs) use a large, powerful battery to move the car. However, they usually also have a smaller car battery, just like gasoline cars. This smaller battery powers the standard 12-volt accessories, like the lights, radio, and wipers. These are often called auxiliary batteries.
Unlike regular cars, EVs don't use an alternator to charge this auxiliary battery. Instead, they have a special device called a DC-to-DC converter. This converter changes the high voltage from the main EV battery down to the 12 volts needed for the auxiliary battery.
History of Car Batteries
Early cars didn't have batteries. Their electrical systems were very simple. They used bells instead of electric horns, and gas lamps for headlights. To start the engine, you had to use a hand crank.
Car batteries became common around 1920 when cars started using electric starter motors. A special "sealed battery," which didn't need water added often, was invented in 1971.
The first car electrical systems used 6 volts and were "positive-ground." This meant the car's metal frame was connected to the positive side of the battery. Today, almost all cars use a "negative-ground" system, where the negative side of the battery is connected to the car's chassis.
The Hudson Motor Car Company was the first to use a standard battery size in 1918. This standard was set by the Battery Council International (BCI), which still sets battery size rules today.
Cars used 6-volt systems until the mid-1950s. The switch to 12 volts happened because newer, bigger engines needed more electrical power to start. Some smaller cars, like the Volkswagen Beetle and the Citroën 2CV, kept using 6-volt systems for a bit longer.
In the 1990s, there was talk of switching to a 42-volt electrical system. This would have allowed for more powerful electric parts and lighter wiring. However, with better electric motors and new ways to control car systems, along with the rise of hybrid cars, this change didn't happen.
How Car Batteries Are Made
A car battery is a type of "wet cell" battery, meaning it uses liquid. It has six connected parts, or cells. Each cell has plates made of a lead alloy. Some plates are filled with sponge lead (negative plates), and others are coated with lead dioxide (positive plates). Each cell is filled with a sulfuric acid solution, which is the liquid electrolyte.
In the past, each cell had a cap where you could check the liquid level and add water. These caps also had a small hole for hydrogen gas to escape during charging.
The cells are connected by thick metal straps. Two large terminals, usually at the top, connect the battery to the car's electrical system. Older car batteries used hard rubber cases and wooden separators between the plates. Modern batteries use plastic cases and woven sheets to keep the plates from touching and causing a short circuit.
Maintenance and Types of Batteries
In the past, car batteries needed regular check-ups to add water, which would evaporate. Newer "low-maintenance" or "zero-maintenance" batteries use different materials for the plates. This reduces how much water is lost during charging. Many modern batteries don't need extra water during their lifetime.
However, a downside of these batteries is that they don't handle being completely drained very well. If the battery dies, like when you leave the lights on, it can damage the plates and shorten the battery's life.
VRLA batteries, also known as absorbed glass mat (AGM) batteries, are better at handling deep discharges but cost more. You cannot add water to VRLA batteries. They have a special valve that releases pressure if the battery is overcharged. VRLA batteries also won't spill their liquid, which makes them good for vehicles like motorcycles.
Most car batteries have six galvanic cells connected in a series circuits. Each cell provides about 2.1 volts, so a fully charged 12-volt battery actually has about 12.6 volts. When the battery is being used, a chemical reaction happens inside that releases electrons, creating an electric current. As the battery discharges, the acid reacts with the plates, changing their surface to lead sulfate. When the battery is recharged, this reaction reverses, and the plates return to their original state, ready to be used again.
Some cars use different types of starter batteries. For example, some Porsche 911 GT3 RS models and all Kia Niro hybrid cars from 2018 use lighter lithium-ion batteries. Heavy vehicles might use two batteries connected in series to get a 24-volt system.
Battery Specifications
Physical Size
Batteries are grouped by their physical size, where their terminals (connection points) are, and how they are mounted in the car.
Amp Hours (Ah)
Ampere hours (Ah) tells you how much energy the battery can store. It's a way to measure its capacity. For example, a 100 Ah battery should be able to provide 5 amps of power for 20 hours at a certain temperature, while keeping its voltage above 10.5 volts. Keep in mind that the faster you use the power, the less total capacity the battery will have. Colder temperatures also reduce capacity.
Cranking Amperages (CCA, CA, MCA, HCA)
These numbers tell you how much power a battery can deliver to start an engine, especially in different temperatures.
- Cold Cranking Amperes (CCA): This is the amount of current a battery can provide at 0°F (about -18°C) for 30 seconds, while keeping its voltage at or above 7.2 volts. Modern cars start very quickly, so CCA numbers are less critical than they used to be.
- Cranking Amperes (CA): This is similar to CCA, but measured at 32°F (0°C).
- Marine Cranking Amperes (MCA): Also measured at 32°F (0°C), this rating is often found on batteries for boats or lawn mowers, which are less likely to be used in freezing conditions.
- Hot Cranking Amperes (HCA): This is the current a battery can provide at 80°F (26.6°C) for 30 seconds, maintaining at least 7.2 volts.
It's important not to mix up these ratings. A 250 CCA battery will have more starting power than a 250 CA (or MCA) battery, and a 250 CA battery will have more than a 250 HCA battery, because colder temperatures make it harder for batteries to deliver power.
Group Size
The Battery Council International (BCI) sets "group sizes" for batteries. This specifies the battery's physical measurements, like its length, width, and height, to make sure it fits correctly in different vehicles.
Date Codes
In some countries, batteries have codes to show when they were made. This helps you buy a fresh battery, because batteries slowly lose charge while they are stored. For example, a battery made in October 2015 might have a code like "10-5" or "K-5" (where "A" is January, "B" is February, and so on, skipping "I").
Using and Maintaining Your Battery
Too much heat is a major reason why batteries fail. High temperatures can make the liquid inside evaporate, which damages the battery. Cold temperatures can also cause problems.
If your battery is too low to start the engine, you can jump start the car using another vehicle or a special power source. Once the engine is running, it can recharge the battery, as long as the alternator and charging system are working fine.
Rust or dirt on the battery terminals (the connection points) can stop your car from starting because it creates electrical resistance. You can prevent this by applying special dielectric grease to the terminals.
"Sulfation" happens when the battery plates get covered with a hard layer of lead sulfate. This makes the battery weaker. Sulfation can occur if a battery isn't fully charged and stays discharged for a while. Sulfated batteries should be charged slowly to avoid further damage.
SLI batteries (starting, lighting, and ignition) are not designed to be completely drained. Doing so can significantly shorten their lifespan.
Car batteries that use lead-antimony plates used to need regular refilling with pure water. Newer designs use calcium in the plates, which greatly reduces water loss. Modern car batteries need less maintenance, and some don't even have caps for adding water. These batteries have extra liquid inside to last their whole life.
Some battery makers include a small hydrometer built into the battery. This little window shows you how much charge the battery has.
The main way batteries wear out is when active material flakes off the plates. This material collects at the bottom of the cells and can eventually cause a short circuit. This problem can be greatly reduced by putting one set of plates inside plastic bags made of a special material that lets liquid and ions pass through but stops the flaked-off material from building up.
Environmental Impact
Battery recycling of car batteries is very important. It means we don't need to dig up as many new materials to make batteries, and it keeps harmful lead out of landfills. It also prevents dangerous ways of getting rid of old batteries.
A used lead-acid battery (ULAB) is considered hazardous waste because of the lead inside. The 12-volt car battery is actually the most recycled product in the world! In the U.S., about 100 million car batteries are replaced each year, and 99 percent of them are recycled. However, sometimes recycling is done in places without proper safety rules, which can still cause pollution. About 97 percent of the lead in old batteries can be recovered and reused. Experts estimate that millions of people in developing countries are affected by lead pollution from improper battery recycling.
See Also
In Spanish: Batería de automóvil para niños
- Anderson Powerpole connectors
- Automobile auxiliary power outlet ("cigarette lighter receptacle")
- Battery charger
- Battery tester
- Deep-cycle battery
- Lead–acid battery
- VRLA battery (AGM and gel cell)
