Jump Starting Your Vehicle Safely
Where possible it is best to use a dedicated battery charger to replenish the charge. Only use the jump start method as a last resort.
There are some essential basics you need to know before jump starting your vehicle. Getting it wrong could end up more costly than the price of a battery. This doesn’t just apply to the vehicle being jump started but the one you’re getting the boost from and your own personal safety – batteries can explode! Be wary of passing traffic if on the side of a road.
Connecting two vehicle batteries Ensure both vehicles use the same voltage battery. For the vast majority of cars/vans this will be 12v. Larger vehicles may start to use 24v.
Note the location of the batteries in each vehicle and the length of your jumper/booster cables. If they are not long enough to reach you will have to park the donor vehicle the best way possible to do so.
Ensure both cars are switched off. Also make sure heater fans, heated windscreen switches, lights etc are all switched off. Basically anything that will be zapping charge.
Lay out the cables on the floor. Make sure they are not touching the bodywork on either vehicle or touching each other. Grab one pair (red and black) and start connecting to the flat battery first in this order: First connect the red connector to the positive terminal. This can be identified in two ways. It will usually have a large red cable going to it and also have a + sign stamped on that side of the battery. Ensure the clip is making a good connection. Now connect the black lead to the negative (-) terminal.
Now pick up the other pair, ensuring they do not touch. Connect the red clip first to the donor car’s battery. For the black clip, do not connect it to the battery post but to a suitable earthing point on the car which is bare metal. Ideal locations are engine mounting brackets or other good solid metal brackets attached to the engine, preferably away from the battery – batteries can give off flammable gas and making the last connection will usually result in a spark. Note vehicles with their batteries in the boot/trunk can be more susceptible to gas build up.
Now start the donor car’s engine and leave it running for 3 minutes. This will start providing some charge to the flat battery. It will help speed up the charge if you keep the engine revs at around 2k.
Keeping the engine of the donor car revved (if there are two of you) go to the vehicle with the flat battery and attempt to start the engine. Once it starts you have two options:
1) Start removing the cables in this order. Go to the flat battery vehicle and unclip the negative (black) cable. Then the red positive. Make sure they do not touch other and lay them on the ground. Now go to the donor vehicle and remove the red positive cable and then the black negative
2) The other option is to leave both cars running and the cables connected for 5 to 10 minutes. Switch both engines off and remove the battery cables in the same order. The reason for this option is because according to some sources removing cables while engines are running may cause spikes and damage to ECUs. Personally I’ve never experienced this issue but I will leave it to you to judge. Whenever I’ve even seen roadside rescue operators (the very ones who advise this on their own website!) they never turn the engine off when releasing the battery clips. Largely I think it is important that when you release the first clip you do so quickly and cleanly, ensuring you don’t touch it again.
Driving the car a good distance will usually start charging up the battery to a decent level but if it is in a very poor state you’re best advised to drive straight home or wherever is safest rather than risk being stranded again. An extremely poor battery may not charge at all and be totally dead if you turn off and try to restart.