Every vehicle owner should know how to test a car battery. There are many car batteries today that no longer require periodic maintenance. This does not mean that they will last forever. That is why everyone should still know how to check the condition of the battery in one’s car. You can do this by using either a multimeter or a hydrometer. We will explore these two methods in this article to help you learn how to check car battery.
Testing with a Multimeter
Some of the world’s best car battery testers are digital multimeters. They work best on so-called maintenance-free batteries. This type of battery does not have caps that one can open to gain access to the different chambers or ‘cells’ of the battery. They are sealed units, preventing the leakage of electrolytes on the surface of the battery.
Multimeters measure the voltage, resistance, and electric current present in an electric device. Since batteries hold an electric charge, a digital multimeter can measure the current state of charge of the battery. This will give you an idea whether your car battery has enough charge to perform its intended functions. If you have the best ATV batteries or the best motorcycle batteries that are of the maintenance-free type, then a multimeter is for you.
Learning how to test a car battery with a multimeter is easy. Before you start testing the best car battery or the best RV battery, however, it is best to familiarize yourself with the functions of your digital multimeter. Different manufacturers may have different styles. However, they all include a mechanism for selecting the different features of the device. Read the manual so you will have an idea as to how to operate the multimeter.
The multimeter comes with two electric connectors with metal probes. The wires come in two colors: black and red. The black-colored wire is negative while the red-colored wire is positive. It is very important to remember what these colors indicate. You do not want to connect either metal probes on the wrong battery terminal.
If you are going to test car battery with digital multimeter, set the device to DC or direct current. Be sure to set it to 20 volts. A healthy car battery should have a charge of about 12.6 volts. Setting the multimeter to 20 DC volts is sufficient.
Get the black metal probe and touch the tip to the negative battery terminal post. Get the red metal probe and touch the tip to the positive battery terminal post. The resting voltage of a healthy battery is about 12.6 volts. If you ask an assistant to turn on the headlights of the car, you will see a drop in the voltage reading in the multimeter. It can be 12.5 volts.
If the battery’s resting voltage reads 12.3 volts, then you can say that it contains about 75 percent of electric charge. If it is not higher than 11.8 volts, then the battery is less than 25% charged. These readings are at an ambient temperature of 80 degrees Fahrenheit.
It is also important to remember that there is such a thing as ‘parasitic loss’. There will always be some car components that use electricity even though the engine is already turned off. The computer, digital clock, security system, and other components can still draw power from the battery. This can lead to a reduction in the battery’s charge over time.
If you test car battery with digital multimeter and the reading is less than the ideal charge, you may want to remove the battery. Recharge it using a battery charger. Leave the battery to rest overnight. Test it again the following morning. If it is able to hold the ideal charge, then it is possible that something in your car is draining the battery a lot faster. You may want an automotive electrician to take a look at your electrical system.
Testing with a Hydrometer
If you have a battery that comes with caps, then you have a standard automotive battery. The caps serve as access to the chambers that contain the battery cells. Inside the battery is an electrolyte solution that contains a mixture of sulfuric acid and water. Be very careful if you are going to test such batteries. The acid can corrode metal, especially the clamps and bolts of the battery cables and terminal posts. Acids can also burn the skin.
For those who are interested in learning how to test a car battery using a hydrometer, you will need a simple gadget that measures the battery liquid’s specific gravity. The device will not tell you how much voltage is in your battery. Instead, it will tell you if it is fully charged, faulty, or undercharged. It is best to use a hydrometer that already comes with a built-in thermometer. This will make it a lot easier to also measure the temperature of the battery fluid.
When checking your battery using a hydrometer, it is ideal to use safety goggles. Opening the caps will release fumes from the battery. These can get in your eyes and cause a burning sensation. You will also need a pair of gloves that can resist acids. As mentioned, sulfuric acid can burn the skin.
Remove one battery cap at a time. Insert the hydrometer’s tip through the hole and submerge it in the fluid. Squeeze the bulb of the hydrometer to push air out. Release the hydrometer bulb so that some of the electrolyte solution will enter the needle of the hydrometer. Read the specific gravity. Remove the hydrometer from the hole and replace the cap. Write down the specific gravity reading on a piece of paper. Do the same procedure on the rest of the cells of the battery.
In a healthy battery, the specific gravity should read from 1.265 to 1.299. Any value that falls within this range will indicate that the battery is holding a good charge. If the reading is below 1.265, then the battery is undercharged.
Compare the specific gravity readings across all the cells of the battery. It is okay if they vary by a bit. However, if there is a difference of about 0.025 to 0.05 between cells, there is a chance that the car battery is already sulfated. Replacing your battery is the only recourse in sulfated systems.
Checking the Battery Terminals
There are certain situations where the battery itself is not the problem. Rather, it is the battery terminals. If it is corroded, loose, or dirty, you will still have issues starting your engine. It is also one of the most common reasons why people think their car battery is already dead.
The good news is you can also use a multimeter to check if you have faulty battery terminals. To do this, you will have to disable your car’s ignition system. The easiest way to disable the ignition system will be to remove the relay or the fuse for the fuel pump. Another method will be to disconnect the ignition coil. Any of these methods will prevent the car engine from starting.
Get the red metal probe of the multimeter and place the tip on the positive battery terminal post. Now get the black metal probe and put it on the same battery post. Ask someone to turn on the car engine. Watch the needle or the display of the multimeter. If you read more than 0.5 volts, there is a chance that the positive battery terminal is dirty or corroded.
Do the same procedure on the negative battery terminal post. You need to touch it using the black metal probe first before the red metal probe. Let your assistant crank the engine. If you see a voltage reading that is higher than 0.5 volts, then there is a problem in your battery terminals.
It would be best to examine the battery terminals a lot closer. Check for any sign of damage, corrosion, or accumulated dirt. Clean it well and check again.
Checking the Alternator
The alternator is an important component of the vehicle’s electrical system. It helps charge the battery while the engine is running. It can also produce electricity by converting the mechanical energy from the engine into electrical energy. This can help power the different electrical components of the car and take the load off the battery.
You can use a multimeter to check the state of your car’s alternator. Perform the same test as in how to test a car battery with a multimeter. Check it with the engine running at idle speed this time. Your multimeter should read anywhere between 13.8 volts and 14.4 volts.
If it is lower than 13.8 volts, then your car’s battery is undercharging. If it is higher than 14.4 volts, it is overcharging. Either of these situations can shorten the lifespan of the battery. You may want a mechanic to check the alternator or an automotive electrician to assess your car’s electrical systems.
Every vehicle owner needs to know how to check car battery. You can use a multimeter if you have a maintenance-free type of battery. If the vehicle runs on older batteries, then a hydrometer will suffice.