How to boost your car battery safely

The long-term solution may be a new battery but the immediate one is a set of jumper cables

Published: January 5, 2015, 12:25 AM
Updated: November 30, 2021, 11:57 AM

Battery Boost

Vehicle won’t start? The only sound you hear is a clicking noise? It's Murphy’s law in action: you will never experience a dead battery in summer with plenty of time on your hands, but count on it at the worst possible moment on the coldest day of the year. The long-term solution may be a new battery but the immediate one is a set of jumper cables and a donor vehicle.

Precautions when boosting a battery

Before you connect those cables and try to start your vehicle pay heed to a few extremely important safety issues:

  1. Sparks: Even a seemingly dead battery will maintain some charge and the one in the donor vehicle will have plenty so there is a real potential for a short or sparking if the cable are mishandled.
  2. Damage: Improper connections can not only be dangerous, they can fry some very expensive electronics, so pay attention and take your time.
  3. Acid: Batteries rely on a corrosive combination of acid and water to store electric energy. Be extremely careful of any transfer of material from the battery to your hands or clothes, especially that powder-like white or light green stuff around the terminals where you will be connecting the cables.
  4. Protection: Wear eye protection and gloves if at all possible.

Before you start boosting a car battery

Now that you've taken the correct precautions you should be ready start, but before you start you should follow these steps:

  • Check the booster cables for any sign of damage such as loose connections or bare wires and repair if required.
  • Locate the battery in your vehicle. It's usually under the hood and to one side. If it's not there, check the owner's manual as it may be under the cargo floor or even the rear seat.
  • Do the same for the donor vehicle.
  • Pull the donor vehicle close enough that the booster cables will connect to the two batteries with some slack in the cables.
  • It is safest to shut the donor vehicle off until the cable connections are complete.
  • Locate a red cover marked positive ( ) and a metal post marked negative (-) on the battery. On some vehicles there is provision under the hood for booster cable connections without actually accessing the battery.
  • If possible, recruit a helper to provide a second pair of hands to handle the other end of the booster cables. The two ends of the booster cable will each have a red and a black clamp. Each person should take the red side in one hand and the black in the other being very careful to never let them touch each other. Do not let any cable clamp touch either vehicle.
  • The order in which you make the connection between the two batteries is very important.

Follow these steps carefully when boosting a car/truck battery

  1. Connect one red clamp to the positive ( ) terminal of the dead battery.
  2. Connect the other red clamp to the positive ( ) terminal of the donor battery.
  3. Connect one black clamp to the negative (-) terminal of the donor battery.
  4. Connect the other black clamp to any solid piece of unpainted or bare metal that is part of the engine or body structure, as far away from the battery as possible. Bolts and brackets make good connection points.
  5. Caution Do Not connect that black clamp directly to the negative (-) terminal of the dead battery. Doing so might cause a spark and resultant explosion from gases escaping from the battery. Most modern batteries are fully sealed but leakage may occur if the battery is damaged.
  6. Stop and double-check that all connections are secure.
  7. Ask your helper to rev the engine in the donor car slightly – not to an extreme.
  8. Try to start the vehicle with the dead battery. With modern electronic ignition and fuel injection systems it is not necessary to press on the accelerator or take any other steps. If the engine turns over easily but still does not start there may be something else wrong. Don't continue to crank the engine without result as doing so could damage the starter motor or electrical system.
  9. Once the dead vehicle starts, after breathing that sigh of relief, take time to finish the job safely. Let both vehicles idle for a few minutes and then disconnect the cables in the reverse order they were connected. Remember to prevent any of the four cable ends from touching each other or either vehicle.
  10. Do not shut off the vehicle with the discharged battery until you have driven far enough for it to be recharged by the vehicle's alternator. Typically, 25 kilometres or half an hour should recharge it sufficiently to restart. Note that it may not recharge if the engine is just idling, particularly if lights, heater fan or other accessories are on.
  11. If the battery is more than a couple of years old perhaps it may be a good idea to have it checked at a service outlet with the equipment to conduct a load test. It may be time for replacement.

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