How many Amps in a Car Battery: Despite being one of the most important components in a car’s engine, many people are unfamiliar with their battery. We all know that car batteries have a voltage of 12 volts, but how many amps does a car battery have – and what does that even mean?
Knowing how your battery works will help you troubleshoot any issues that arise. We’ll go over how to determine a battery’s ampere rating as well as how to charge it to get the most power.
Everyone wants to keep their car in the best possible condition, and part of that includes understanding how cars work. Most people have a basic understanding of some parts, but others, perhaps not so much – and the battery falls into that category.
We’ve all heard terms like “volts” and “amps,” but what exactly do they mean? Which are the most important? As we ask, how many amps is a car battery?, we’ll try to answer these and other questions.
Before you continue reading, you can watch this video for a preview of some of the topics we’ll be discussing.
How many Amps in a Car Battery
A typical car battery has a capacity of approximately 48 amp hours, which means that when fully charged, it delivers 1 amp for 48 hours, 2 amps for 24 hours, 8 amps for 6 hours, and so on.
A basic charger typically charges at around 2 amps, requiring 24 hours to deliver the 48 amps required to fully charge a flat, 48 amp hour battery.
However, there is a wide range of chargers on the market with varying charge rates ranging from 2 to 10 amps. The faster a flat battery is recharged, the higher the charge output. Fast charging, on the other hand, is not recommended because it can cause the battery plates to buckle.
The amount of current used by various electrical components can be used to calculate the load on your battery: headlights take about 8 to 10 amps, a heated rear window about the same.
In theory, a fully charged battery should power the starter for about ten minutes, the headlights for eight hours, and a heated rear window for 12 hours without drawing power from the generator. As the battery nears full discharge, the lights gradually dim and eventually go out.
Car Battery Maintenance Infographic
Car Battery Specifications and Features
To understand what your car’s battery can and cannot do, you must first understand its chemistry, voltage, capacity (Ah), Reserve Capacity, CCA (Cold Cranking Amps), MCA/CA (Marine Cranking Amps/Cranking Amps), HCA (Hot Cranking Amps), PHCA (Pulse Hot Cranking Amps), and so on.
– Chemistry: most car batteries are tested and reliable lead-acid batteries, but wet/flooded lead-acid batteries are being phased out in favor of Absorbent Glass Mat (AGM) Sealed Lead Acid (SLA) batteries, which offer greater vibration resistance, spill proof design, maintenance free operation, and other benefits. Lithium-ion drop-in replacements are available as both starting and dual-purpose batteries, but they have not been tested in real-world scenarios as thoroughly as AGM SLA batteries.
– Voltage: Lead-acid car batteries have a nominal voltage of 12 volts, but the actual voltage varies. When the engine is running and the alternator is charging the battery, the common voltage should be between 13.5 and 14.0 volts, and it should never be higher than 15 volts. When the engine is not running, the fully charged AGM battery should have a voltage of 13+ volts – actual voltage may vary depending on the battery and onboard electronic system being constantly online. If the battery voltage falls below 10.8 volts (1.80 volts per cell) and the engine does not start, the battery is deeply discharged.
– Capacity: The capacity of the car batteries is given in Amp Hours (Ah), which describes how many Amps (A) the battery can provide for 20 hours before the voltage drops below a certain level, which is usually 10.5-10.8 volts (1.75-1.80 volts per cell). Draining the battery below this cut-off voltage may result in permanent battery damage.
For example, the capacity of a lead-acid battery is determined by how many amps of current a new, fully charged 12V battery can deliver for 20 hours at 80°F (25°C) without its voltage dropping below 10.5V.
Typical car batteries have nominal capacities of 50-100 Ah, with large diesel-powered trucks frequently having 100+ Ah batteries capable of providing 1000+ CCA.
Nota bene: The Yugo 45’s ‘lawn mower engine’ had a 34 Ah starting battery that could easily start the engine. Of course, if the engine wanted to start 🙂
Reserve Capacity (RC) is the number of minutes that a new, fully charged battery (at 80°F, 25°C) can deliver 25A current while maintaining voltage above its cut-off value (10.5V for lead-acid batteries).
Although Reserve Capacity is more important for deep cycle batteries used in marine applications (for trolling motors, for example), RVs (in-house batteries), solar systems (off-the-grid applications), UPS (Uninterruptible Power Systems), and similar, it is also becoming increasingly important for car batteries.
For example, when the engine is turned off, multimedia systems can drain the battery with relatively high currents – a 200 watt multimedia system can easily draw 20-25 amps from the battery (in some cases even more).
Electric systems with two separate batteries are recommended for even more powerful multimedia systems – one as a starting battery and another for multimedia and other systems.
– Cold Cranking Amps (CCA) is the maximum current that a new, fully charged 12V battery can deliver for 30 seconds at 0°F (-18°C) while the voltage does not drop below 7.2V.
Cold Cranking Amps (CCA) is a critical value for cars, trucks, and other vehicles during the winter, and it is often the first thing to look for when inspecting starting batteries.
– CA (Cranking Amps) or MCA (Marine Cranking Amps) is the maximum current that a new, fully charged 12V battery can deliver for 30 seconds while maintaining a voltage of 7.2V at 32°F (0°C).
The CA/MCA value indicates how well the battery performs in marine cranking/starting applications, where actual battery temperatures rarely fall below 32°F (0°C).
Although 30 seconds may appear to be too long for starting applications, whether CCA or CA/MCA, keep in mind that this is the value for a brand new, fully charged battery. In real life, a battery must function properly even after being used for an extended period of time (months or years) and without being fully charged!
– Hot Cranking Amps (HCA) is the maximum current that a new, fully charged 12V battery can deliver for 30 seconds while maintaining a voltage of 7.2V at 80°F (27°C). It should be noted that some manufacturers provide PHA values measured at different temperatures.
Because HCA is 1.6-1.7x greater than CCA for most AGM batteries, CCA is the most important value for measuring battery strength, even if the battery is not intended for low temperature applications.
PHCA (Pulse Hot Cranking Amps) is the maximum allowed current that a new, fully charged battery can provide for 3-5 seconds at 77-80°F (25-27°C). This is a ‘unofficial’ parameter, but it is frequently used to measure the battery’s starting strength.
Similarly to PHCA, some manufacturers provide values for’maximum pulse drain current,’ which is often given in Amps and seconds, such as 200 Amps for 10 seconds, 100 Amps for 15 seconds, and so on.
– The maximum charging current is the maximum current that can be used to charge the battery without damaging it. Personally, I believe that discharged AGM batteries should be charged for at least 2 hours on a regular basis, with quick charging (less than 1 hour) used only when absolutely necessary, even when quick charging batteries are used. Accuse me of being paranoid, but…
What Is the Difference Between Volts and Amps?
Let us begin at the beginning. What exactly are amplifiers? How about the volts? And how do they differ? Let’s take a look at these questions now, and we’ll do our best to keep it as simple as possible.
In a nutshell, an amp is a unit of measurement for electricity, whereas voltage is the difference in electric potential.
Volts are a measure of the force that causes electrons to flow through a conductor, whereas amps indicate the rate of flow of electrons.
This is all very abstract and difficult to understand, but there is a well-known analogy that can help.
Consider electricity to be like water flowing through a pipe. The current, which is measured in amps, is the rate at which electricity (water) flows. The battery is analogous to a pump that pushes water through a pipe, and the voltage is a measurement of pressure.
When we talk about the amps and voltage of a car battery, we are referring to the “speed” of the electric current (amps) and the “pressure” of that current (volts).
Different Methods of Measuring Amps
One of the issues with determining how many amps are in a car battery is that there are several methods for doing so. Let’s take a look at a few of the most important ones right now.
A unit of measurement used to describe the amount of power that
Using amp hours to measure the amps of a car battery is one of the most important methods. This is a measurement of the battery’s capacity expressed as the amount of time it can produce a current of one amp per hour before it dies.
This means that a car with a 50-amp-hour battery can provide a current of 1 amp for 50 hours. Car batteries have a wide range of ratings, ranging from around 50 amp hours to 500 amp hours.
However, not all businesses calculate amp hours in the same way; for example, some use a 10-hour rate, others a 20-hour rate, and still others a 100-hour rate. Check out the video we included above for a more in-depth explanation of this.
What Is the Reserve Capacity of the Battery?
It’s difficult to discuss car battery amps without mentioning battery reserve capacity. Because the amps in a car battery are classified into three categories (CCA, cranking amps, and reserve capacity), it is critical to discuss what this means when purchasing a new car battery.
Did you know that you can charge your laptop with your car battery in an emergency?
The reserve capacity of a battery refers to how long it can be discharged at a rate of 25 amps. The reserve capacity is also measured in minutes at an average temperature of 80 degrees Fahrenheit. For example, if a car battery’s reserve capacity, or RC rating, is 120, it means the battery can provide 25 amps for 120 minutes before losing valuable power to start the vehicle.
How to Charge a Car Battery
If your battery runs out of power, you can recharge it with a battery charger. These work by recharging the battery with mains power.
Most battery chargers charge at a rate of 2 amps per hour in general. This means they can charge a 48amp battery completely in 24 hours. This isn’t particularly fast, but it’s preferable because it’s better for your battery’s health.
Other chargers that charge batteries much faster are available. Some chargers, for example, can charge at a rate of 10 amps per hour.
However, because they are bad for the battery, using one of these is only recommended when you need to charge it quickly.
Also, be sure to unplug it from the battery once it has finished charging; otherwise, you risk damaging the battery.
Connecting a battery charger
A one-piece cell-cap cover fits in a central trough in some batteries.
Before connecting the battery to the charger, always check the electrolyte level. If necessary, top up the batteries (see Checking the Batteries ) and clean the battery posts.
If a power outlet is nearby, the battery can be left in the car as long as the charge rate is only 3 or 4 amps.
However, if the vehicle has an alternator, disconnect the battery terminals first; otherwise, some alternators, particularly older models, can be damaged.
If separate cell caps are used, they must be removed for ventilation. Unless the charging rate is high, leave the trough cover on. Clamp the positive (+) lead from the charger, which is typically red in color, to the positive battery post. Connect the negative (-) lead, which is typically black, to the negative terminal.
Connect the charger to the power supply and turn it on. The charging of the battery will be indicated by an indicator light or gauge ( ammeter ).
The charging rate may appear high at first, but it will gradually decrease as the battery charges.
If it was very flat, charging will most likely take a long time; check periodically with a hydrometer while charging.
The cells bubble and emit gas in the final stages. If any of them start gassing before the others, or if they start gassing more violently, the battery is most likely defective and should be checked by a garage or battery specialist.
Before disconnecting, unplug
After charging, always turn off the power and unplug the charger before removing its terminal clips; otherwise, the clips may spark as you remove them, igniting gas released during charging.
When reconnecting the battery, make sure no electrical circuits in the car are turned on – a spark may occur as you replace the second battery terminal and ignite battery gas.
Car Battery Charger Varieties
A basic home battery charger uses a transformer and rectifier to convert the mains 110/220 volt alternating current to 12 volt direct current, allowing the mains supply to provide a charging current at a rate determined by the battery’s state.
With a standard home charger and a good battery, the rate of charge may be around 3 to 6 amps.
A battery nearing the end of its useful life may not accept recharging and, in any case, will not hold a charge.
Some chargers include a high and low (Hi-Lo) switch that allows you to choose between two charging rates – typically 3 or 6 amps – in case you want to give the battery a quick overnight boost at 6 amps rather than a longer charge at 3 amps.
Many have a charge indicator, which can be either a warning light or a gauge that shows the charge rate in amps.
It should be noted that the mains lead on all chargers should be fused. If it isn’t, a three-pin fused plug should suffice. Fit a line fuse cable lead to the battery as an extra precaution.
How Do You Read And Understand Car Battery Specifications?
Car battery specifications adhere to standards developed by the Battery Council International (BCI) and the Society of Automotive Engineers (SAE). Many of the specifications can be found on the standard battery label or sticker, as well as in the published literature of battery manufacturers. The following are the most important specifications for car enthusiasts:
CCA: The discharge load in amperes that a new, fully charged battery can deliver at 0 degrees F for 30 seconds while maintaining a voltage of 1.20 volts/cell or higher. This metric assesses a battery’s ability to start (crank) an engine under low-temperature conditions in which the chemical reaction inside the battery slows: A battery produces 100 percent of its rated power at 80 degrees Fahrenheit, 65 percent at 32 degrees Fahrenheit, and only 40 percent at 0 degrees Fahrenheit. CCA is a great way to compare battery performance in cold climates, but in hot climates, lead-acid batteries with extremely high CCA ratings may have a shorter life than those with lower ratings: Increasing the CCA within a given overall battery case (group) size necessitates thinning out the internal plates in order to squeeze more out of them within the same case volume. Thinner plates are prone to vibration and overheating.
Cranking Amps (CA): The discharge load in amperes that a new, fully charged battery at 32 degrees F can deliver continuously for 30 seconds while maintaining a terminal voltage of 1.20 volts/cell or higher. CA ratings can be deceptive because they can be up to 30% higher than equivalent CCA ratings. According to the BCI, a battery with a statement of CA performance must also list its CCA capacity.
Reserve Capacity (RC): If listed, this is the number of minutes a new, fully charged battery can be discharged at 25 amps while maintaining a voltage of 1.75 volts/cell or higher at 80 degrees F. RC is the number of minutes a 12-volt battery (six cells) can maintain a voltage of 10.5 volts with a 25-amp draw; thus, a “75-minute” battery lasts 75 minutes under these conditions. The larger the RC, the better; modern cars with numerous accessories can see current discharge rates far exceeding 25 amps.
Amp-Hours (AH): This one is a little more difficult. This is sometimes referred to as the “C20” rating and can be found on a deep-cycle battery sticker. It is a measurement of how much energy a battery can provide continuously for 20 hours at 80 degrees Fahrenheit without dropping below 10.5 volts. A battery rated at 100 amps/hour will provide 100 amp/hours of power, or 5 amps per hour. However, as BatteryStuff.com points out, in practice, “The relationship between total discharge time and applied load is not linear. As load increases, so does realized capacity. This means that if you discharged the same 100 amp/hr battery with a 100 amp load, you would not get one hour of runtime. On the contrary, the battery’s perceived capacity will be 64 amp-hours.”
Deep Cycle: This refers to the torture test that, if passed, allows a battery to truly call itself “deep cycle.” It lasts more than 100 hours and is an SAE-specified measurement of the battery’s ability to withstand repeated discharge/recharge cycles. The severe test provides the most accurate overall assessment of automotive battery performance under extreme operating conditions. Because of the severity of the test, this information is generally not published, with the exception of batteries specifically designed for “deep-cycle” service. Deep-cycle batteries are typically used in race cars without alternators that require a recharge between rounds, or in a street car that sits in a parking lot for hours with a high-amp stereo system turned on and the engine turned off.
Date Code: Most batteries have a date code, which is typically a long string of numbers and letters that indicates when the battery was purchased. One row of one- or two-letter codes represents the month, while the other row of numbers represents the year’s final digit. At the time of purchase, the relevant date code in the ID should have been stamped or highlighted.
Group Size: According to BCI, this is the standard “envelope size” of the battery case, which equates to its height, width, length, and terminal position. Physically, batteries with the same group number interchange. In many cases, the group size is part of the battery manufacturer’s part number.
Important Car Battery Specifications
- Cold Cranking Amps (CCA): A measurement of the battery’s cranking ability at 0 degrees F
- Cranking Amps (CA): A measurement of the battery’s cranking ability at 32 degrees F
- Reserve Capacity (RC): The number of minutes a battery can be discharged at 25 amps
- Amp Hours (AH): How much energy a battery can deliver continuously for 20 hours
- Deep Cycle: A 100-hour test of a battery’s ability to withstand repeated discharge/recharge cycles
- Date code: A string of numbers and letters found on many batteries that show when the battery was purchased
- Group Size: Standardized classification defining a battery’s physical envelope and terminal position
Is it better to charge my car battery at 2 amps or 10 amps?
It is best to charge the battery slowly. Slow charging rates vary depending on the type and capacity of the battery. When charging an automotive battery, however, 10 amps or less is considered a slow charge, while 20 amps or more is considered a fast charge.
When a 12 volt battery is fully charged, what voltage should it read?
approximately 12.6 to 12.8 volts
A fully charged battery should have a voltmeter reading of 12.6 to 12.8 volts. If your voltmeter shows a voltage between 12.4 and 12.8, your battery is in good condition. Any voltage greater than 12.9 volts is an indication that your battery has an excessive voltage.
How do you calculate a battery’s current?
Multiply the Ah by the nominal voltage to get Wh. For example, suppose we have a 3V nominal battery with a capacity of 1Amp-hour, resulting in a capacity of 3 Wh. 1 Ah means that we can theoretically draw 1 Amp of current for one hour, 0.1A for ten hours, or 0.01A (also known as 10 mA) for one hundred hours.
Is it safe to leave a car battery charger plugged in overnight?
Even if there is no risk of overcharging when using a high-quality charger, the battery should not be left connected to the charger for more than 24 hours. Charging overnight usually results in a full charge. Even after a deep discharge, some chargers allow for at least partial battery reconditioning.
How long does it take to charge a 12 volt car battery at a rate of 2 amps?
How Long Does It Take To Charge A Car Battery At 2 Amps? Charging a car battery with a 2amp charger will take a long time. It takes about 24 hours to fully charge a 48amp battery using this type of charger.
Is 11.9 volts sufficient to start a car?
The normal voltage required to start the car is 12.6 volts. This parameter is between 13.7 and 14.7 volts at the time of exploitation.
What is the minimum voltage for a 12 volt car battery?
12.0 volts or less – Your battery is considered fully discharged or ‘flat’ at 12.0 volts and should be recharged as soon as possible. If you leave your battery in this voltage range for an extended period of time, it will have a short lifespan.
Battery Council International (BCI); Chicago, IL; 312.245.1074; BatteryCouncil.org
BatteryStuff.com LLC; Grants Pass, OR; 800.362.5397 (orders) or 541.474.4421 (tech); BatteryStuff.com
Exide Technologies; Milton, GA; 800.START.IT or 678.566.9000; Exide.com
Interstate Batteries; Dallas, TX; 866.842.5368 (customer service) or 888.772.3600 (tech); InterstateBatteries.com
SAE International; Warrendale, PA; 877.606.7323 or 724.776.4970; SAE.org