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Is your car’s battery dead or weak and unable to start the car?
There is plenty of advice out there on how to jumpstart a car using jumper cables but not enough clarity on whether you can use another battery and jumper cables to charge the dead or weak car battery and its limitations.
In this post, I will cover:
- whether you can actually charge a car battery with jumper cables,
- the advantages,
- how to do it safely
and what alternatives there are.
Can you Charge a Car Battery with Jumper Cables?
Yes, you can partially charge a dead or weak car battery by connecting it to a charged battery using jumper cables.
Make sure though that the jumper cables are connected right and firmly to the battery posts, i.e. the positive terminal posts of both batteries should be connected together and the battery negative terminal post using the jumper cables for charging to start.
To fully charge a car battery, you need a higher voltage of 14.5 VDC for AGM batteries that cannot be provided by a fully charged battery with its 12.6-12.8 VDC.
You can achieve this fully charged stage with a good quality external charger with the correct battery setting for your battery type or your car’s alternator after your car has started and has been driven for about 15-30 min.
Why Using Jumper Cables can be a good idea
Using jumper cables and a good battery isolates the electrical system of the car with the weak battery from the higher currents from the other car’s alternator.
This can be an issue if you are attempting to jumpstart a small car with a larger car – truck, or van with the engine running.
Disadvantages of using Jumper Cables
It does not charge the battery fully, it is only partial – you need to drive the car to top up the charge or use an external charger to do so.
You may need to wait for about 5-15 min or longer until the weak battery has charged enough to start the other car.
How to Safely Charge a Car Battery with Jumper Cables
To charge a weak or dead battery safely, follow the correct order of connecting and disconnecting the jumper cables outlined below.
Order of Connecting Jumper cables
1. For the car with the good battery, first, connect the red (positive) clamp of the jumper cable to the positive battery terminal (marked with a + sign).
2. Connect the second red clamp of the jumper cable to the positive battery post of the dead battery (marked with a + sign)
3. Next, connect the black clamp to the negative post (marked – sign) of the good battery.
4. Finally, connect the second black clamp of the jumper cable to the exposed, unpainted part (inside the hood) of the car with the dead battery.
Allow the dead battery to charge for about 5-10 minutes and then attempt to start the car with the dead battery.
The car engine may not start on that first attempt. Allow for another 5-10 minutes and try to start again.
It should start normally on the second attempt.
Let the car engine of the car with the dead battery run for about minutes to charge some more and then disconnect the jumper cables in this order.
To Disconnect the Jumper cables
1. First, disconnect the black clamp of the jumper cable from the exposed, unpainted part (inside the hood) of the car with the dead battery.
2. Next, disconnect the black clamp from the negative post (marked – sign) of the good battery.
3. Then disconnect the red clamp of the jumper cable from the positive battery post of the dead battery (marked with a + sign)
4. Lastly, disconnect the red (positive) clamp of the jumper cable from the positive battery terminal (marked with a + sign) of the good battery.
5. Drive the car with a drained battery for about 15-30 min to top up its charge level.
Alternatives to Charging the Car battery with Jumper Cables
# 1. Use a Good quality External Charger. Besides connecting to a good working battery using jumper cables, you can also use a good quality external battery charger.
Make sure it is set to charge the type of battery that your car has – AGM or otherwise.
Unlike using jumper cables, an external battery charge has the following advantages:
- It fully charges the battery unlike when you use a set of jumper cables and another good battery
- It can charge the dead car battery faster. Depending on the charger type and recommended maximum charging current, you may be able to charge your battery using 20, 10, or 5 A moreover fully.
- Good quality external chargers usually have advanced features like the repair mode suited to reviving batteries whose voltages are extremely low or that may not accept charge.
- External chargers can also monitor the temperature of the battery being charged and makes the necessary adjustments so that the battery is charged optimally depending on the prevailing temperature.
# 2. Use a Jumpstarter box or pack. You can also use a charged jumpstarter box that you connect to the dead battery terminal posts.
How Long it Takes to Charge a Car Battery with Jumper Cables?
Depending on how depleted it is, a weak car battery can gain enough charge to start the car engine in about 10 – 15 min of being connected to a charged battery.
Do not expect it to charge fully though!
A dead battery will take longer to pick up enough charge and you may have to use an external charger instead to speed up the charging process.
Can you Charge a Car Battery Out of the car with Jumper Cables?
Yes, you can charge a car battery out of the car also with jumper cables connected to another charged battery in the car.
It is not necessary to disconnect the dead or weak car battery from the car for you to use this charging method.
The important thing is to properly connect the jumper cables, i.e. red clamp from the battery’s positive post to another and a black clamp from the battery’s negative post to that of the second battery.
The battery will be charged only partially.
To fully charge the car battery, you can connect it to an external charger or drive the car for 15-30 minutes.
While you may be able to charge a weak or dead car battery by connecting it to a charged battery using jumper cables, this method does not charge the battery fully.
To fully charge the battery, you can either drive the car for at least 15-30 min after it has started so that the alternator tops up the charge or use an external charger to charge it.
Besides using an external charger, you can use a jumpstart pack or box to jumpstart your car before using the alternator or external charger to top up its charge.