Car batteries are one of the most important pieces of equipment in your auto. Without a working well-maintained car battery, your engine will not start, your lights will not operate, and all of the electronics in your car will not operate.
Batteries decline over time naturally depending on their use and how well they are taken care of. The average life of a battery appears to be approximately five years. However, their age can vary a great deal depending on the environment, how often the car is used, and how well they are maintained.
Sure signs of an electrical problem with either the battery or the charging system is an engine that is slow to crank when starting and dim lights while the engine is idling.
Many batteries become depleted if the alternator is not working properly, many short trips deplete the battery, or there is corrosion around the battery terminals. How do you test a battery’s health, and how many volts should a car battery have?
What is a good voltage reading on a car battery?
Most people refer to a typical car or truck battery as a 12-volt battery. However, when measured, the measurement is never 12 volts. With the engine turned off, the typical battery should show a voltage range somewhere between 12.4 Volts and 12.6 Volts. If you measure the voltage of the battery while the engine is running, the voltage will range between 13.7 to 14.7 volts.
A measurement of fewer than 12.4 volts indicates that the battery is not fully charged. If you measure below 5 volts, the battery is finished, and you should purchase another. Older batteries decline as they age.
Fully charge a battery, obtain the necessary voltage measurement after it has been charged, let it sit for 12 hours with nothing attached. Measure the voltage again, 12 hours later. If the voltage has declined, your battery cannot hold a charge and should be replaced.
How many voltages does a battery need for a car to start?
A cold-cranking amp is a standard measure for a battery. Ideally, the measurement should be taken at zero degrees Fahrenheit and should be able to provide sufficient cranking for 30 seconds without dropping below 7.2 volts.
If you connect the voltmeters on the battery with the engine off, it should read 12.4 to 12.7 volts. As the engine is started, the voltage will drop to around 10 to 10.5 volts. This is normal and acceptable.
Once the engine starts, the alternator begins generating electricity to charge the battery and run the accessories. The voltage measured after the engine starts should be 13.0 to 14 volts.
If the battery voltage drops below 10 volts while starting the engine, the battery is starting to fail and could leave you stranded along the road at some point. Below 5 volts, it is time to replace the battery.
How do you perform a load test?
A load test is another way to check your battery’s health. Load testers are not expensive; however, they are specialized testers that can only be used for this purpose vs. using a multimeter which is much more versatile.
Follow the instructions that come with the load test device. Attach the electrodes to the battery positive and negative terminals making sure to attach the cables as per the instructions that come with the device.
The load tester will place a load on the battery for approximately 30 seconds. Make sure the battery is fully charged before making this test. The battery should not fall below 9.6 volts during the test. A battery that falls below 9.6 volts is not in great shape and should be replaced.
Whenever you are working around a battery performing car battery testing or cleaning terminals, always wear hand and eye protection. The corrosion around the terminals is acidic and could burn your hands and eyes.
What voltage is low for a car battery?
Several voltages indicate a bad battery. They are listed as follows:
- With the engine running – 13 to 14 volts is considered normal
- With the engine off – 12.4 to 12.7 is considered normal
- Cranking the engine – no lower than 10 volts
- Battery load tests – battery voltage should not fall below 9.6
- Failing battery – any measurement that does not meet these specifications
- Failed battery – 0 to 5 volts.
A battery that is older than four years should be checked at regular intervals to avoid the battery failing and leaving you stranded. Accessories provide a battery drain and can quickly cause even a new battery to exhibit these measurements. Recharge the battery and retest it.
Before replacing the battery, particularly if it is a new battery, confirm that the alternator is providing sufficient power to recharge the battery. Your battery may be fine even though it is exhibiting these low voltages because the alternator is not providing sufficient power.
How do you know if you need a battery replacement?
Always confirm that the alternator is providing sufficient power to charge the battery. With the engine off, test your car battery. The battery voltage should read 12.4 to 12.7 volts, and as it starts, the violated will decline to around 10 volts then spring back to 13 to 14 volts.
These measurements indicate your alternator and your battery are fine. A fully charged battery should hold a charge overnight. If the voltage declines even though the battery is not connected, it is a sign it is beginning to fail. A battery voltage measurement below 5 volts is a sure sign that the battery is failing.
Performing a load test over a 30 second period using a load tester should indicate if the battery has sufficient cranking amps. If the battery voltage falls below 9.6 volts during the load test, it indicates the battery is beginning to fail. While it may still start your car’s engine, it is only a matter of time before it fails.
Top 5 Things That Will Probably Kill Your Battery
Even if your battery is brand new several things will deplete your battery and cause it to fail at the most inopportune time. Usually, that is when you are heading to work, picking up the kids, or late for an appointment. Avoiding the following can preserve your battery and not leave you stranded.
Extreme outside weather
Extreme cold weather can reduce the energy in a battery and cause it to produce fewer cranking amps than normal. In addition, your engine is cold and difficult to start, placing a heavy load on the battery. Cranking the engine to continue to start can quickly deplete the battery. A weak battery can also freeze in these conditions, making it useless and needing to be replaced.
Elevated parasitic draw
Elevated parasitic draw is the current drawn by various components in your vehicle while the engine is turned off. A healthy battery can provide this power with little problem, however leaving the lights on, running the radio for an extended time, and leaving power to the accessories on can quickly drain the battery leaving it incapable of starting the engine.
Leaving your headlights on
Today many cars automatically turn off the headlights a few minutes after the engine has been turned off. Older vehicles may not have this feature and can quickly deplete the battery energy. Even new cars can deplete the battery if the accessory option is turned on. Always make sure the lights are off since this is one of the most common reasons batteries are drained of their energy.
Bad or failing alternator
Your battery may be fine, but if your alternator is not generating sufficient power to run the engine and the accessories, the power comes from the battery and depletes it rather quickly. Check that the fan belt is still in place and have your alternator checked. The check engine light will be illuminated in most cases if you have a failing alternator.
Corroded battery terminal
Corroded battery terminals are another indicator of a battery that is slowly losing power. The connections may be corroded and not allowing sufficient power to be delivered to the starter. Remove the cables from the battery and clean them with a wire brush. Avoid allowing the cables to touch each other or the opposite terminals of the battery to avoid shorts and arcing.
Are 11.9 volts enough to start a car?
A well-tuned engine that usually starts easily should be fine with a battery measuring 11.9 volts.
It does indicate that the battery is not fully charged. It should be charged immediately by going on an extended drive since many short trips can gradually deplete a battery. The battery voltage should not fall below 10 volts, and it may not be able to start your car’s engine in extreme weather conditions.
A cold environment depletes the battery, and the engine is more difficult to crank in very cold weather. You may find that your engine does not start in some of these extreme conditions.
Recharge your battery, make sure all of the accessories are turned off in your car and measure the voltage. Wait 12 hours and re-measure the voltage. If the voltage falls below the normal threshold of 12.4 volts again with no load, it is a sure sign that your battery is beginning to fail.
How many volts should a car battery lose overnight?
A healthy auto battery should not lose any volts overnight. There are several reasons why a battery could be discharging and losing voltage in a short period, for example, overnight:
- Accessories were left on
- Headlights or parking lights were left on
- Battery plates can no longer hold a charge
- Corrosion around the terminals is providing a high resistance load
- An old dead battery
A battery that cannot hold a charge overnight should be replaced. The battery cannot be relied on to providing sufficient cranking amps and voltage to start your engine. Many drivers have recharged a battery, completed a test start of their engines, only to find the battery cannot start the car the next morning.
All they get is a clicking noise from the starter. Remember to always recycle old batteries. Most battery shops have programs for this and will provide a discount when you bring in your old battery.
What causes a car battery to lose voltage?
Most batteries lose voltage for several reasons, which include the following:
- Corroded terminals can bleed off voltage and amps
- Lights or accessories left on with the engine off and draining the battery
- Older batteries that can no longer hold a charge, even after being fully charged
- Anytime there is a high resistance short which can drain the battery
- Continuous engine cranking in extreme cold weather and the engine will not start
- Many short trips where the battery is not fully recharged
- A malfunctioning alternator that is not charging the battery
- A broken fan belt that also runs the alternator
Any of these conditions can cause the battery to indicate a lower voltage than normal when tested. The battery may not have sufficient power to crank the engine when starting leaving the driver stranded and in need of a battery jump start.
If you notice any of these things, have your battery tested before you are left stranded on the road and need to have your vehicle towed to a garage.
How low should battery voltage drop while starting your car?
The battery voltage should not drop below ten volts while starting your vehicle’s engine. Attach a multimeter to the battery terminals set to measure voltage. With the engine off, it should read between 12.2 volts and 12.7 volts with no surface charge.
As you start the engine, note the voltage drop. If it drops below 10 volts, there may be a problem with the battery, and it should be tested by completing a battery load test.
Once the engine starts, the alternator begins generating electrical power, and the voltage should quickly return to a normal operating voltage above 13 volts and as high as 14 volts. If your battery was fully charged and now cannot start the engine, it is likely dead unless there has been a draw on the battery overnight.
Test by fully charging your battery, let it sit for 12 to 24 hours, disconnecting the battery avoids any outside load on the battery, and measure the voltage. Anything less than 12 volts suggests it is not holding a charge and should be replaced. A reading of 5 volts or less indicates a dead battery and must be replaced.
How often should you test a car battery?
New batteries do not need testing often, however as they age, regular testing can help to avoid being left stranded. There are several ways to test the battery. However, the easiest by far is to observe the brightness of the lights when the engine is idling.
The headlights should be bright and should not dim when the engine idles. If they do, there is something that should be checked in the charging system, including battery health.
You can have your battery tested when regular vehicle maintenance is performed or once every six months. Many drivers will perform their tests using a multimeter. Set the meter to twenty volts DC and connect the black lead to the negative terminal and the red lead to the positive terminal. If you read a negative number, switch the leads.
With the engine off, the battery should read in the range of 12.4 to 12.6 volts. Anything less than that indicates the battery is not fully charged. This could be caused by a failing battery, a failing alternator, or too many short trips, and the battery has not had sufficient time to fully recharge from many engine starts.
It is recommended to test a car battery monthly after the first year and prior to storing a vehicle for an extended period of time. With regular testing, you can find out if your battery needs to be replaced or if the alternator is not charging the battery.
Car Battery Voltage Tips
The battery is part of the charging system in your car and provides power to the car’s electrical system in the vehicle. A dead battery can leave you stranded at the worst possible times. Have your battery tested regularly, usually during maintenance updates such as oil changes and tune-ups?
The battery’s voltage observed on a fully charged battery should be between 12.4 and 12.7 volts. A reading lower than this number suggests the battery is not fully charged and may not be able to start your engine. Batteries typically last from five to seven years, depending on the conditions they are subjected to. Many drivers replace their batteries at the 5-year mark to avoid being stranded on the road.
In addition to voltmeter readings, load testers can be completed at a battery testing site to confirm the condition of your battery. Car battery voltage voltmeter readings less than 10 volts indicate that the battery is severely discharged or must be replaced if it cannot be recharged. A battery tester or multimeter is inexpensive.
Before replacing your battery, have your alternator tested to ensure the charging system is working. Your check engine light and trouble codes generated by the computer system in your vehicle may indicate the alternator has failed. Always make sure your car’s accessories are off to avoid fully discharging your vehicle’s battery.
Remember that the positive terminal will have a red plastic cover, and the negative terminal will have a black plastic cover. Using a multimeter will give you a more accurate measurement than just using a voltmeter. A multimeter measures both voltage and resistance in electrical circuits.