Is a Car Battery AC or DC?

Car batteries are a direct current (DC) power source since their electrical current only flows in one direction.
Written by Amber Reed
Reviewed by Melanie Reiff
Car batteries are considered a direct current (DC) power source because their electrical current flows in one direction—from the battery’s positive terminal to its negative terminal.
Trying to understand your car’s electrical system can be a little intimidating, but learning about the battery is a great place to start. While most car engines are powered by gasoline or diesel fuel, it’s the battery that handles the most crucial car function—its ignition system. Your car’s battery is also the sole power source for things like your headlights, automatic windows and locks, power-adjustable seats, audio system, and navigation system.
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Is a car battery AC or DC?

All car batteries use direct current, or DC, power. This is the same type of power found in all common battery types, including household lithium-ion batteries. Because DC electricity only moves in one direction, it can be stored in a battery to move high amounts of power.

Direct current vs. alternating current

There are two types of electrical power transmission you should be aware of: direct current (DC) and alternating current (AC)
In alternating current power systems, chemical energy is converted into an electrical charge that periodically changes polarity along with the voltage—which also reverses to match the charge. Alternating current was first put to use by Nikola Tesla when he invented the power transmission system in 1888, and it continues to be used today for things like microwaves and other appliances with higher voltage. In general, AC power is more efficient than DC power, but you cannot store AC power in a battery.
A direct current, on the other hand, generates a constant flow of electricity that always moves in one direction. Invented by Thomas Edison in the 1880s, it has the ability to be stored inside a battery, where a chemical reaction occurs to create electrical energy. This type of current can move large amounts of electricity at a relatively low cost—making it particularly efficient in a car, which needs to run for long distances without losing power. 
Today, DC power is used in most electronic devices, low-voltage appliances, and virtually anything that requires a battery in order to run.

How a car battery works  

Most cars are powered by a 12-volt lead-acid battery. Inside the battery, lead plates are immersed in sulfuric acid to cause a chemical reaction. The chemical process generates ions, which move around the lead plates and create an electrical current. The current then moves through the wires connected to the battery and reaches your starter motor, ignition system, and other automotive components.
One of the main things that makes lead-acid batteries special is the fact that they are rechargeable, which makes
jumpstarting your dead car battery
possible. Inside your car, a mechanism called an alternator recharges the battery by creating an electrical current, transmitting it to your engine through the alternator belt, and converting physical energy into electricity through a component called a rectifier. While some of this converted electricity is used to power your car’s electrical systems, some of it is sent back to the battery. This battery charger system is why car batteries can last for years before they need to be replaced. 
Key Takeaway A car battery uses a chemical reaction to generate electricity, which is then distributed to the car’s starter motor and ignition system.
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Signs that it’s time to replace your car battery

On average, it takes about three to five years before you need to
replace your car battery
. If you’ve had the same battery in your car for a while, it’s a good idea to have the battery inspected by your preferred mechanic, or keep an eye out for signs that your battery is getting low on power
Here are a few things to watch out for.
  • The battery light is on. If you have a newer vehicle, an illuminated battery icon on your dashboard will let you know when you’re low on power.
  • Your headlights or dashboard lights get dim when you idle. This can be a sign that your battery is struggling to generate the electricity needed to power your car. 
  • Your car stalls out in cold weather. Cold temperatures slow down the chemical reactions in your battery. A fully-powered battery handles temperature fluctuations better than one that’s about to die. 
  • It’s hard to start your car if you haven’t driven it in a while. If you went out of town (or simply haven’t driven in a few days) and find your car is struggling to start, then you might need to replace its battery. 
  • There’s corrosion or leaking fluid on the battery itself. A functioning battery should always look clean. If your battery is corroded or leaking, it’s either old or low on power and should be replaced.
  • Your engine doesn’t turn over immediately. If you start your car, and your engine cranks for a few seconds before the car actually starts, your battery’s power could be depleted. 

How to find cheap car insurance  

Watching for the warning signs can help you catch a dying battery—but there are some cases where a car battery might fail without warning. Getting stranded with an inoperable car can be frustrating, but that’s where
roadside assistance coverage
comes in to play. With this coverage, your
car insurance
covers the cost of towing your car to the mechanic and getting a new battery installed. 
Want to add roadside assistance to your current plan? Or just want cheaper car insurance?
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Every car uses a DC current 12-volt lead-acid battery.
Vehicles can’t run on AC power alone, since both combustion and electric cars are powered with direct current (DC) batteries; however, AC current is used in combination with the battery to power other parts of the car such as the alternator.
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