How to Start a Car with a Weak Battery
When you start your car, a couple of things happen. First, the battery has done its hardest job, causing the engine to turn over. Second, the alternator automatically takes over the job of recharging the battery, using the power ultimately drawn from your engine.
That’s the good news: in most cases, you just need for the engine to turn over, and for the alternator to have time to recharge your battery, for your weak battery problem to go away.
To get the engine to turn over, there are two tried and true methods. We’ll start with the method that works on all internal-combustion-powered cars, the jump start.
Jumping a car with a weak battery transfers a charge from a stronger battery to yours. For this you need a charging source (usually another car) and jumper cables to get the current from that source to your battery.
First, the charging car should not have its engine running.
Next, identify the positive and negative terminals on the top of your battery. These are identified by the “+” sign and “-” sign on the cables that attach your battery to your electrical system, and/or on the battery terminals themselves or nearby on the plastic cover of the battery. Sometimes it is difficult to find the “+” or “-”, and you may have to wipe away some grime. But persevere. You cannot go forward until you locate one of these symbols!
Once you locate either symbol, the other one applies to whichever terminal is left over: they come in matched pairs. There are no batteries with two positive or two negative terminals.
Jumper cables come with one red cable and one black cable ending in large alligator-style clamps on either end. Throughout the process, take great care that the ends of these cables do not make contact with each other.
Next, identify the terminals on the other vehicle’s battery. If your rescuer is identifying the other battery’s terminals, make sure you communicate which color cable means positive. Conventionally, red is positive and black is negative – but make sure you both agree on this!
Using red as positive: attach the red cable to both batteries’ positive terminals. Attach the black cable to the charging battery’s negative terminal. and to a ground on the car with the weak battery (such as the engine block).
First, the “rescue” starts his car and revs its engine. Then you do likewise. When your car starts, the rescuer has done all he can. For your part, keep your engine running 20 minutes to half an hour, to allow the alternator to charge your battery.
There are also emergency jump boxes that can stand in for the rescue car. These cost from $70 to $100, and come with built-in cables. At the very least you should carry jumper cables with you.
If your car has a manual transmission, you have one other option: the venerable push-start technique.
To push-start your manual transmission car, start with the clutch pushed down. Put the car in first or second gear – or, if you are parked front-end-highest on an incline, put it in reverse. Make sure lights, radios, and wipers are off, and the key is in the start position.
Someone has to push the car until it gathers enough speed to “pop the clutch.” Usually this is possible at about five miles per hour, but the faster you are going, the better. Take your foot off the clutch, and the car should start. Be ready; at this point your car will be running and in gear.
NOT RECOMMENDED: To push-start the car alone, you can begin with the car in neutral in place of using the clutch. Steer with one hand, brace yourself against the frame of the car with the other, and push the car up to speed. Then shift from neutral into first or second gear. Again, this is a less safe push-start maneuver and should not be attempted if there are any other options.
As with the jump-start method, the alternator will take over once your car is running. And as with the jump-start method, you should leave the engine running or drive the car around for 20-30 minutes.