How To Jump Start A Car
Returning to your car to discover the engine will not start as the battery is flat is not uncommon. The chances of this happening can be greatly reduced if simple routine steps are followed. Our car battery maintenance guide explains this in detail.
In order to start your car with a flat battery you are going to need an external 12 volt power source in the form of another car or battery booster. If you are going to use the power from another car, Make sure it is the same voltage which is normally 12 volts. You will also need a heavy duty set of jump leads to provide enough current to start the engine. If you have access to a battery booster you will not need jump leads or another car as most car battery boosters are equipped with all you need to start your engine from a flat battery.
What is a car battery booster?
A battery booster is essentially a 12 volt battery which unlike a normal wet car battery, they normally have a rechargeable 12 - 20mAh / 12 volt sealed lead acid battery inside a plastic housing with handle. This battery can either be charged from the mains at home or from the cigarette lighter socket. On the unit you normally have a meter or row of LED lights which show the charge state of the battery and warn if needing charged. Two heavy duty jump leads exit the unit for connection to the flat battery. A battery booster is connected in the same way as you would connect the battery of another vehicle. However, we recommend you follow instructions in the user manual which may show connection methods specific to the device.
Step 1: Park Cars In Safe Area
If possible, park both cars away from traffic and place a warning triangle nearby to alert other road users of the situation. Apply handbrake and place in Park (P) if cars has automatic transmission.
Step 2: Open Bonnet Of Both Cars
With both cars now secured, pull bonnet release catch normally located under steering column, above pedals or in driver or passengers footwell. Get out the car and pull bonnet up and secure with prop rod.
Step 3: Check Condition Of Flat Battery
With the bonnet now open, check the condition of the flat battery for signs of corrosion or leaks. Do not attempt to jump start the vehicle if the battery is damaged due to risk of explosion. Obtain a new battery and replace at the roadside making sure to dispose of the old battery at your local recycling centre.
Step 4: Clean Battery Terminals
If battery terminals of either vehicle are dirty, clean them with a wire brush in order to improve electrical contact between battery and jump leads.
Step 5: Connect Flat Battery
Connect positive red (+) jump lead to positive red (+) terminal on the flat battery taking care to observe polarity, + to + and - to -.
Step 6: Connect Charged Battery
Connect other end of the positive red (+) jump lead to the charged battery. Again, take care to observe polarity.
Step 7: Connect Negative Lead To Charged Battery
Connect one end of the negative black (-) lead to the negative black (-) terminal of the fully charged battery.
Step 8: Connect Negative Lead To Earth
Connect other end of the negative black (-) lead to a bare metal, unpainted part in the engine bay away from the battery such as a bolt, engine component etc.
Step 9: Start Engine Of Fully Charged Battery
Start the engine of the car which has the good fully charged battery and allow the engine to idle at around 1500 to 2000 RPM for 5 minutes in order to allow time for charge to enter the flat battery. Keeping the engine at a fast idle will increase charge into the flat battery as the alternator will be spinning faster providing more electricity to the circuit.
Step 10: Start Engine Of Flat Battery
Now attempt to start the engine of the flat battery and allow to run at a fast idle - 1500 - 2000 RPM for a further 10 minutes to allow the battery to return to a fully charged state. If the car still will not start, do not keep trying as this will prevent the battery from charging. Allow another 5 minutes for the cars battery to charge off the donor cars battery and try again.
Finally remove jump leads from both cars and close bonnet. Because your car battery has been fully discharged, this normally dramatically shortens the life of the battery so it may be a good idea to get the battery checked at you local garage. Many larger nationwide garages offer this service for free so be sure to get it checked before this happens again, because it will.
Happy safe motoring, hope you enjoyed the guide.
3 Responses to “How To Jump Start A Car”
By Jayson on May 8, 2008 | Reply
You mentioned to connect the jump lead for the Negative to the bare metal of the car with the flat battery and NOT to the Negative terminal of the flat battery - why is that?
Will it damage the battery if both the Posative AND Negative are connected the terminals of the flat battery??
By admin on May 8, 2008 | Reply
No, it’s not that it will damage the battery, it is for risk of fire/explosion.
When you complete the circuit by connnecting the two car batteries, the potential difference (voltage) and the amount of current drawn from the good battery causes a spark which can cause explosion by igniting gases from the battery’s acid.
It is for safety reasons you connect to a negative ground metallic object. The bodywork of a car is directly connected to the (-) terminal of the battery anyway.
Hope this helps. If there is anything else i can help with, let us know.
By Andy Jones on Sep 28, 2008 | Reply
I’ve known cars that have been able to start on their own at Step 4, after cleaning up the connections to the battery terminals, and checking the started solenoid connections too. I’d not heard that the reason for going onto the negative ground metallic object was to have the spark away from the flattened battery, but that is a sensible precaution. Instead, I understood that if you connect onto a suitable lug on the engine, you bypass what might be a poor connection between the flat battery and the car’s bodywork, improving the prospects for the starter motor (and possibly reducing the inrush current to the flat battery). From financially painful practical experience, I now make sure that at step 9, the guy with the flat battery doesn’t try to start his car at the same time as I’m starting mine - buckled battery plates and two dead cars was the result. Also, I prefer to switch off the charging engine before letting the other person try starting their car, to spare the diodes of my alternator. Is that being overly cautious?