Although electrical shock is a possibility when jump-starting a car, you also need to be careful so that the battery doesn’t explode, spraying acid onto everyone and everything nearby.
If your car won’t start, you may want to jump-start it so you can drive it to a mechanic or recharge the battery. But before you attempt to jump-start a car, you need to determine if the battery is really the problem. If the headlights or other lights still work, the battery isn’t dead, and jump-starting won’t help. Jump-starting the vehicle is also not the answer if the motor cranks, although the battery may be partially drained if the engine turns over sluggishly a few times.
Before you connect the jumper cables, get ready by following these steps:
- Park a running vehicle near the car with the dead battery, but not so close that the two vehicles are touching.
- Put both vehicles in park (or neutral for vehicles with manual transmissions), and be sure both parking brakes are on.
- Turn off both vehicles and anything that would use electricity: fans, lights or audio equipment.
- Remove any corrosion from the battery posts (the short metal rods coming out of the battery) or the bolts that attach wires to the battery. Special metal brushes are available for this, but you probably don’t carry one in your vehicle, so do your best to brush or scrape off the corrosion.
- Check the dead battery for leaks or cracks. If the battery is damaged in any way, don’t try to jump-start the vehicle.
- If the battery is not the sealed type (see the Image Gallery for examples of different types of batteries), pry off the caps (or unscrew them) and make sure the battery has enough water in it. It’s rare to have to add water to modern batteries, but the water level should be up to the bottoms of the holes that the caps fit into. If it doesn’t have enough water in it, add distilled water. Do not try to jump-start the battery if the liquid in it is frozen or the water level is too low.
Car batteries contain acid, so you can get an acid burn if you touch the liquid inside the battery. It will also eat holes in clothing. Wear safety goggles and gloves.
Connecting the Jumper Cables
Your vehicle’s owner’s manual should have information on jump-starting (or tell you not to jump-start it). If you can’t find the battery easily, the manual will tell you where to attach the jumper cable clamps.
Don’t allow the clamps to touch each other while you are connecting them to or disconnecting them from the batteries.
Batteries create hydrogen, which can build up and, if ignited, explode. (Do not smoke while jump-starting a vehicle.) When an electrical circuit is being closed, there is a possibility of creating a spark. This procedure for connecting jumper cables minimizes sparks near the batteries:
- Connect one red clamp to the positive (+) post of the dead battery.
- Connect the other red clamp to the positive post of the good battery.
- Connect one black clamp to the negative (-) post of the good battery.
- Connect the other black clamp to bare, clean metal away from the battery of the dead car. Brackets or bolts on the engine are usually good places to connect the clamp, but check the owner’s manual for suggestions.
Most jumper cables have red and black clamps, but if your set uses different colors, that’s OK. If you have cables with yellow and black clamps, for example, replace the word “red” in the above instructions with “yellow.”
Before starting either vehicle, be sure the jumper cables won’t be damaged by moving parts (fans, belts or pulleys) when the cars are running. Close vehicle doors so dome lights don’t draw power.
Run the engine of the vehicle that starts for about three minutes. Then try starting the vehicle with the dead battery. After it starts, disconnect cables in reverse order from when you connected them and drive the car for about 30 minutes to charge the battery — if you turn it off before the battery charges, you’ll have to jump-start it again. The other option is to drive it to a mechanic who can check it over or charge the battery for you.
If the vehicle doesn’t start after a few tries, give up; you may have a different problem. Disconnect the cables in reverse order.
Download a free, printable copy of How to Jump-start a Car to keep with your jumper cables or in your glove box.
Do you have other tips for jump-starting a car? Post your suggestions in the comments section below.