How many volts should a battery read

How do I use a multimeter to test a car battery?

Testing a car battery with a multimeter is a simple process. The first thing to do is make sure you can access the two terminals on the top of the car battery.

Car batteries are commonly located in the engine bay to one side of the engine, and often have a plastic cover which will unclip, lift off, or occasionally require the removal of a couple of bolts. There may also be a cover over the positive (+) terminal, which usually lifts off.

Once the car battery is exposed be careful that nothing metal touches the terminals, so don't rest any spanners or other tools on it.

Using your multimeter, you want to measure DC voltage (this is indicated with a solid line and a dashed line above a letter V). Set the dial to 20. This will allow you to accurately measure 0-20 volts.

Hold the red probe to the positive terminal and the black probe to the negative terminal. The terminals will be marked '+' and '-'. If you're getting a reading with a minus in front of it (-12.6 rather than 12.6) you've got the probes the wrong way round.

The resting voltage should ideally be no lower than 12.6V. Bear in mind that when a battery goes down to 12.2V it's actually only 50% charged, and below 12V it's classed as discharged.

What do I do if the car battery is repeatedly going flat?

If the battery is continually going flat, it could be because of a 'parasitic loss'. This is where something electrical - a light or a motor for example - is draining the battery, even with the engine turned off. Apart from doing the obvious (setting your phone to record video before you place it in the boot or glovebox to see if the bulb is staying on), you can either remove the leads from the battery, or remove it from the car entirely.

Then, fully charge the battery, leave it for 12 hours and test it. If the battery holds a charge when it's not connected to the car, it's not faulty.

TOP TIP: Before you disconnect your battery make sure you know the code for your stereo – otherwise you may find it won't work when you reconnect it!

How do I test a car battery for dead cells?

Many new car batteries are of the sealed 'maintenance-free variety. But some older batteries allow you to access the individual cells. The cells will either have individual caps, or a plastic cover that clips over all, or some of the cells.

The cells contain a mix of water and sulphuric acid, so you don't really want to be messing around inside them too much.

You can buy a hydrometer-style battery tester that measures the specific gravity of the battery acid, and can tell you whether any cells are 'dead' or not.

However knowing a cell is 'dead' is of no more use to you than knowing that the battery won't hold a charge, so a test of the resting voltage is just as effective a diagnosis.

Will cold weather affect my car’s battery?

Very cold temperatures will harm a lead-acid or glass mat battery's ability to hold its charge, but the biggest enemy during the winter is the demand that's placed on it by heated screens, the car's heater, heated seats, headlights, heated steering wheel and so on.

Head here to see what you can do to keep your battery in the best of health during winter.

If you make lots of short journeys in the winter with lots of these electrical extras turned on, the alternator is going to struggle to get enough charge back into the battery - and next time you try to start the car there may be zero charge left.

If you have started to notice some issues with your vehicle and suspect your battery might be at fault, how do you diagnose it? Signs of a failing car battery can include trouble with the electronics, dimmed headlights and, of course, being unable to start your car.

If you want to check whether the issue is down to your car battery, there are a couple of tests you can run to help diagnose this. The most important one is simply to check if your car battery is fully charged. You can also read about which type of marine battery is best for boats.

How to Measure a 12 Volt Battery Voltage at Rest

To measure the voltage on your car battery you will need to use a tool called a multimeter. These are relatively inexpensive and can measure voltages, resistance and current on electrical items.

First, you’ll need to find your car battery, these are often in the engine compartment of your vehicle, but on some models, they can be found in the boot.

To connect the multimeter to your car battery you’ll need to first disconnect the terminals from the battery and connect the wires from the multimeter. To do this, remove the positive terminal cover first and connect the positive lead from your multimeter to the battery. Once this is done, you can remove the negative terminal cover and connect the negative lead from your multimeter to the battery.

After you have your multimeter connected you’ll need to turn it on and check the reading.

What Voltage Should My 12v Battery Show?

A fully charged 12 volt battery should read at 12.6 volts on the multimeter. If the reading is lower than this, you’ll want to charge your battery with either a battery charger or by taking your car for a drive.

If your voltage is lower than 12.6 volts by a small margin, this can have a big impact on the car’s performance. For example, at 12.4 volts, your battery will be at roughly 75% charge. At 12.2 volts it will be at 50% charge and at 12 volts it will be at roughly 25% charge.

If your battery is reading around 25% charge, this is a very low reading which will usually result in your car not starting.

What Voltage Should My 12v Battery Show When the Car Is Running?

It’s important to be aware that once a car is running, the voltage you will see from the battery will be higher than when at rest. This will typically read somewhere between 13.7 volts to 14.7 volts depending on the battery.

This is why you should check the battery reading while the car is at rest for the most accurate 12 volt battery reading.

You will also notice that when you initially start the vehicle, the voltage will drop below its initial reading. This is called a cranking test and is a good test to measure the effectiveness of your car battery. A healthy battery should maintain between 9 volts and 10 volts when trying to crank the engine. If your multimeter reads numbers lower than this, you might have a weak battery that could need replacing.

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