Jumping a Battery

Remember the days when you didn't have to think about what to do next if your car battery died? You just pulled out your trusty jumper cables and took care of it. Things aren't quite that simple anymore with modern cars. Nowadays, vehicles have a lot of complex electronics, not just in the dash, but under the hood as well. These electronics can be damaged in a jump start between two cars.

There's also the placement of the battery and whether you should even use it in a jump start. Many car companies have moved the battery away from the engine bay, like in the Challenger. This is to reduce weight over the front end of the car and to keep the battery cooler to prolong its life. So, you have to use remote terminal posts instead of the battery itself when performing a jump start. This helps the protect the car's computers from being fried. Some manufacturers have hooked a battery health monitor up to the negative terminal of the battery.

Hybrids and EVs are their own monsters entirely, with their own set of rules about jump starting (some manufactures even prohibit using them to jump start another vehicle). And then there's the question of whether the donor car should be running while setting up for a jump start. All of this can be resolved, of course, by checking the owner's manuals of both cars involved in a potential jump start. The manual will tell you if your car should be used in a jump start. If there are any special requirements, like using remote terminals instead of the battery, the manual should tell you that, as well.

There always seems to be some confusion about whether the donor vehicle should be turned on. Back in the day, we'd connect the cables while both cars were turned off, then turn on the donor vehicle and let the car with the dead battery sit a little bit and soak up the power from the donor battery before turning on the ignition. Sometimes, we'd rev the donor car to help things along. After a few minutes, we'd try to turn on the dead vehicle. Have things changed for modern cars? No. Just about every manufacturer recommends jump starting cars in that order. Some even included the step about revving the engine of the donor vehicle. But not all cars are the same, so it's important to check your owner's manual to determine whether your vehicle should be turned on when jump starting. Generally, you start with connecting one of the red cables to the positive terminal on the dead battery. Then, connect the other red cable to the positive terminal on the donor battery. Next, connect one of the black cables to the negative terminal on the donor battery. Finally, ground the other black cable to an unpainted metal surface of the dead vehicle, away from the battery.

One word of caution. Jump starting hybrids is risky because they have two batteries- a high-voltage lithium battery that helps power the motor, and a regular 12-volt battery to power all of the traditional parts, like the stereo and ignition. The 12-volt battery also used to start the high-voltage lithium battery. If the hybrid vehicle is jumping or being jumped, make sure you connect the cables to the 12-volt battery, not the high-voltage one. This may be a challenge, since the 12-volt battery can be in the trunk or under a seat. And remember to stay away from anything that is high voltage. Once again, check with your manufacturer first. Kia says point blank, "Do not jump start another vehicle with your hybrid vehicle. Jump starting another vehicle will damage the hybrid vehicle's 12-volt battery." So, read your owner's manual.

What about an EV? Again, check with the manufacturer to learn whether you can use it to jump another vehicle or if its 12-volt battery can be jumped. Tesla says in its Model 3 manual, "Model 3 cannot be used to jump start another vehicle. Doing so can result in damage." Also, you should never use one EV to jumpstart another EV.

What if your owner's manual tells you not to jump start your battery or use it to jump start another car? You can use a portable jump starter instead. The right booster can jump a dead battery faster than another car could. They are fairly inexpensive as well. But more importantly, many of these boxes regulate voltage, prevent feedback, and protect the alternator of the donor car. They work much like jumper cables, but without the second car. You just connect the red cable to the positive battery terminal and the black to the negative, then start your engine, which you should be able to do almost right away. Quickly disconnect the cables and let your car run for several minutes so the alternator can fully charge the battery. The booster itself is rechargeable, and you can do multiple jumps before having to re-charge it.

So, why is a simple jump start such an issue with modern cars? It's partly because new vehicles are built with tiny computers called engine control units (ECUs). These little units manage lots of things, from air intake to ignition timing, and they're sensitive. A jump start with another car can blow one of these units or cause them to reset, resulting in the check engine light turning on and multiple codes needing to be cleared. Jumper cables allow power to flow freely, leaving both cars vulnerable to a power surge, which can cause several problems. Some have reported these surges causing damage to a car's traction control system, power steering, airbag system, and the start/stop system. There's also the possibility of voiding your warranty if you execute a jump start incorrectly.