A car battery is vital to the functionality of a vehicle’s electrical system and to start the engine. If the engine does not start for some reason, it may be that the battery is dead. But does a dead battery need to be replaced, or can a dead car battery be charged?
A dead car battery can be charged to full capacity with a battery charger or by jump-starting the vehicle. The battery can be charged if the car battery has a voltage of 12.71 to 12.06 volts. If the voltage is less than 12.06 volts, the battery will not keep its charge and must be replaced.
Read on to discover how different voltages can determine the charge level of a car battery and the different methods of charging.
Can A Dead Car Battery Be Recharged?
When people say that a car battery is dead, they actually mean that the battery is discharged. A discharged battery does not have enough voltage to crank the engine or run the vehicle’s electrical systems. The good news is that most times, a car battery can easily be recharged and function perfectly.
On the other hand, if the battery is recharged and does not hold the charge (discharged within 24 hours), it will need to be replaced. The best method to test a battery is with a multimeter.
How To Test A Dead Car Battery With A Multimeter
Testing a car battery (12V) with a Multimeter will test the voltage of the battery. If the voltage is adequate, the battery will be able to be recharged. If the voltage is low, the battery will not hold its charge and must be replaced.
To get the most accurate voltage reading, it is recommended to test a battery that has not been used for at least 60 minutes. This is known as the “resting voltage.”
Setting Up The Multimeter
Switch the multimeter on, set it to “20DC volts”. If the multimeter does not have voltage increase settings (2, 20,200), set it to “voltage DC.”
Place the Multimeter Probes On The Battery Terminals
Place the correct probe on the corresponding terminal. The Black probe connects to the negative (-) battery terminal, and the Red probe connects positive (+) terminal.
The Multimeter Readings
Turn on the ignition switch and check the voltage reading on the multimeter.
The following table indicates the charge percentage of the battery.
|DC Voltage Reading||Battery Charge Percentage||Battery Status|
|12.71 volt||Battery 100% charged||Healthy|
|12.51 volt||Battery 90% charged||Healthy|
|12.42 volt||Battery 80% charged||Good|
|12.32 volt||Battery 70% charged||Charge battery|
|12.21 volt||Battery 60% charged||Charge battery|
|12.06 volt||Battery 50% charged||Battery may have burnt cells – replace|
|11.09 volt||Battery 40% charged||Not holding charge – replace|
How To Charge A Dead Car Battery
Recharging a dead car battery can be done by jump-starting or with the aid of a battery charger. Below are the steps to follow for both methods.
Charging A Car Battery With Jumper Cables
Jumper cables are one of the easiest ways to give a discharged battery enough voltage to start the engine. This method is also known as “jump-starting,” and you will need a set of jumper cables and another vehicle with a charged battery.
Step 1 – Position The Vehicles
Position the vehicle with the charged battery near enough to the car with the dead battery so that the jumper cable will breach the gap between the batteries. Ensure that both vehicles are switched off.
Step 2 – Connecting The Jumper-Cables
The jumper cables need to be connected in the correct order. The “Red” jumper cable should connect to the positive terminal of the charged battery, and the other end should connect to the dead battery’s positive terminal.
The black cable should connect to the negative of the charged battery. The other end of the jumper cable should connect to an unpainted bolt or exposed metal part on the vehicle’s engine with the dead battery. Do not connect the negative terminal together, as this will not allow the battery fuses to function correctly.
Step 3 – Start Charging
Switch the vehicle with the charged battery on and allow the car to idle for 5 to 10 minutes to charge the dead battery. Attempt to start the engine in the car with the dead battery while charging. If the vehicle starts, disconnect the jumper cables in reverse order (negative x 2, then positive x 2) while leaving the car with the dead battery idling.
If the vehicle does not start after 2 attempts, allow the battery to charge for a further 10 minutes before trying again.
Step 4 – Drive To Charge The Battery
Once all the jumper cables have been disconnected, allow the vehicle with the discharged battery to idle for at least 10 minutes before driving. It is important to note that the battery voltage will still be low after jump starting. Drive the vehicle for 30 minutes before switching off the engine.
If the battery discharges within 24 hours after jump starting and “drive” charging it, the battery may be damaged and will need to be replaced.
Charging A Car Battery With A Battery Charger
Charging a dead battery with a car battery charger is another easy way to put energy back into a dead car battery, but it does take longer.
- Disconnect all the cables that are connected to the car battery.
- Connect the car charger to the wall power socket, but do not switch it on.
- Connect the red cable of the charger to the positive battery terminal and the black cable to the negative.
- Switch on the battery charger. Select the “slow charge” function on the battery charger. If the charger does not have this function, it should do this step automatically.
- Allow the charger to charge the battery for 6 to 24 hours before removing the charger.
- Once the battery is charged, connect the car’s cables back to the battery terminals starting with the positive cables.
- After connecting the cables, attempt to start the engine.
If the battery discharges within 24 hours after charging it, the battery may be damaged and will need to be replaced.
How Long Does A Dead Car Battery Take To Charge?
The time it takes to charge a dead car battery will depend on the charging method and the battery size( Amps). When using a battery charger to charge a car battery to 100%, it should take between 6 to 24 hours.
This is because most smart battery chargers are rated at 2 Amps (4A, 10A & 20A chargers are available), thus, they can charge a battery with 2 Amps of power per hour of charging. If the car battery’s size is 48 Amps, it will be fully charged in 24 hours (48 ÷ 2 = 24).
The charging times will be influenced by how many amps are left in the battery before charging commences. It is vital not to overcharge a battery, as this can cause damage to the cells in the battery. Using a smart charger that will turn itself off when the battery is fully charged
The charging time is drastically deduced when charging a car battery with the alternator. This is because the alternator can charge a battery at a rate of 30Amps per hour. So, if the dead car battery’s size is 48 Amps and it is charging at 30 Amps per hour, it should take just longer than 90 minutes to charge fully. ( 48 ÷ 30 = 1.6)
Charging a battery with the alternator is the best way to keep the battery at its peak performance. The alternator will not overcharge the battery and only charges it when needed. Suppose the alternator is faulty and is not charging the battery. In that case, a warning light should illuminate on the vehicle’s instrument cluster.
In this event, it is recommended to have a professional inspect the charging circuit, battery, and alternator.
What Causes A Dead Car Battery?
Below are some examples of what may cause a car battery to drain and become discharged.
- Headlights, park lights, or interior lights are left on while the engine is switched off.
- The alarm, entertainment system, or any electrical system is faulty and does not switch off with the car.
- Loose or corroded battery connectors
- Batteries discharge quicker in extremely cold conditions
- The battery is not being charged by driving due to a faulty alternator
- The engine does not run long enough to charge the battery fully due to constant short drives
- The battery is older than five years