What Is a 12 Volt Battery?

Ken Black

A 12 volt battery is an irregular battery used in specific electronic applications. Of all the types of batteries, the 12 volt battery is one that looks very different depending on its use. In some ways, it is one of the most diverse of all batteries. It can be large or small, heavy or light. In some cases, they may look nearly like regular AA batteries.

12-volt batteries are commonly used as car batteries.
12-volt batteries are commonly used as car batteries.

One of the most common uses of a 12 volt battery is for transportation applications, such as in cars and boats. In these cases, the battery may be able to be recharged as current is only needed to start the vehicle. After that, the alternator takes over and runs the electrical system, if it is functioning properly. The alternator also puts a charge back into the battery.

Smaller outboard motors may have a pull start, and have no need of an electrical system for its main motor.
Smaller outboard motors may have a pull start, and have no need of an electrical system for its main motor.

The sizes of 12 volt batteries vary widely based on the amp hours they are designed to produce. They can be very heavy and large, such as those found in cars. They can also be relatively small, such as batteries found in some electrical children's vehicles that run in the front yard.

Most car batteries are lead acid 12-volt batteries.
Most car batteries are lead acid 12-volt batteries.

A 12 volt battery is available as a non-rechargeable alkaline battery or in rechargeable forms. This battery is often used in various outdoor applications that require greater amounts of energy in order to operate as desired. However, it may be recommended to use a rechargeable battery if the electronic item is one that is used regularly. Non-rechargeable batteries can become quite expensive if they must be purchased regularly. Many manufacturers have attempted over the years to reduce the size of the 12 volt battery to one that is easily portable, as some outdoors enthusiasts like to use them to run things like fish finders.

A portable 12 volt battery is usually sealed in a waterproof case.
A portable 12 volt battery is usually sealed in a waterproof case.

While such electronic devices can be run using an electrical system onboard a boat, there are some anglers who do not have an onboard electrical system. Smaller craft with smaller outboard motors may have a pull start and therefore have no need of an electrical system for its main motor. Therefore, running things like fish finders and oxygenators off a separate battery is the only way to do it.

Alternators charge a vehicle's battery and supply its electrical system with power.
Alternators charge a vehicle's battery and supply its electrical system with power.

In such cases where a 12 volt portable battery is used to replace an onboard 12 volt battery, it is usually lighter than a standard version. This is because it is more likely to be transported between uses and consumers will not choose to carry a large, bulky battery. Further, a portable 12 volt battery is usually sealed in a case so that it is waterproof. This is vital, especially in cases where there are boating applications and a substantial amount of water could ruin the battery.

What Should a 12 Volt Battery Read When Fully Charged?

A 12 volt battery is the name given to a unique style of battery, but its voltage is more than 12 volts. When a product of this type is completely charged, it should measure approximately 12.6 volts between the terminals. To know what the voltage of your battery is, you should take a measurement once it has rested for a few days after charging.

A Completely Charged Battery

Immediately after a 12 volt battery is charged in full, it can read up to 14 volts. This gives maximum power to the item requiring energy. It can stay at this voltage for only a few seconds unless you keep it plugged into a charging device. The voltage diminishes without a constant charge as the attached device draws out the battery's energy.

A Deep Cycled Battery

Ideally, a 12 volt battery shouldn’t be allowed below 50% of its power, or 12.5 volts, before recharging. If you must use a battery in an emergency and don’t charge it, the resting voltage can get as low as 12.1 volts before drawing out all power. This indicates that the part has been deep-discharged. A rechargeable battery can only last through so many deep discharges before you can no longer replenish it. This can be up to 180 times for a golf cart and as low as 20 times for a car.

How To Test a 12 Volt Battery

Many devices that depend on a 12 volt battery have a voltage gauge attached. These meters let you know the status of the component to an approximate value. However, if you want a precise measurement to the tenth of a volt, purchase a digital meter. To take an accurate reading, remove any devices that pull power from the battery and let it rest for a minimum of 12 hours. Your digital meter can then display the current voltage. The following is an approximate value of how charged the battery is based on the voltage readout:

  • 11.9 volts, 0 %
  • 12.0 volts, 25%
  • 12.2 volts, 50%
  • 12.4 volts, 75%
  • 12.6 volts, 100%

How Long Does a 12 Volt Battery Last?

The time a battery lasts depends on the amount of energy an attached device is withdrawing, how charged the battery was before use, and if there is an automatic recharging source. A battery can be used repeatedly over many years and recharged numerous times with proper care.

AMPs and Discharge

Various 12 volt batteries are rated for different amps. An amp is a time measurement that lets you know approximately how long the battery can last on a full charge. For example, a 100 amp battery lasts five hours when a connected device draws 20 amps per hour, or 10 hours if it only draws 10 amps per hour. Most batteries have a maximum amp and cannot give more power than rated because it overheats. In this example, a 100 amp battery cannot provide 200 amps of power for 30 minutes.

Automatic Chargers

Some batteries are connected to a continued source of energy that provides recharging. You find these in vehicles where an alternator charges the battery and solar chargers. A steady power source allows the battery to remain at about 13.6 to 13.8 volts, which keeps it at an optimal level without over or under-charging.

Maintenance Makes a Battery Last Longer

Over time, you may notice that dust and debris build up on the battery terminals. It’s necessary to clean this off because it pulls energy away from the product. You can use household cleaner on a cloth or a specifically designed battery cleaning spray to remove the dirt.

Keeping the battery charged over 50% ensures it doesn’t get depleted. Make sure you use an appropriate charger that won’t send a large burst of energy to the component. Rapid charging wears down the internal parts of the battery and makes it more difficult for the cells to hold a charge.

Store a Battery at Room Temperature

Keeping your battery at average room temperature extends the life of your product. Temperatures over 90 degrees cause the power box to charge quickly, leading to overcharging. On the opposite end of the spectrum, batteries kept in temperatures below 32 degrees can cause the liquid inside to freeze. A frozen battery has no way to transmit power until it defrosts. Continued exposure to less than ideal temperatures shortens your product’s life.

Some boats use a 12-volt battery.
Some boats use a 12-volt battery.

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Discussion Comments


Can i use a 12-volt car battery on a power wheels? It's a children's little car that runs on 12 volts with chargers.


Can I charge 24V/100A battery with a 1000 watt inverter?


I'm buying a 2300 watt inverter. I would like to know whether I should use a 12-volt battery charger or 24-volt. What is the difference?

Thank you

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