How to Use a Jump Box to Safely Jump-Start a Car

This article explains how to use a jump box to jump-start a car safely. It includes information on possible dangers and instances when using a jump box isn't a good idea.

Safely Using a Portable Car Jump Starter

Using a jump box is safe in most circumstances, although it is possible to damage both your car and yourself. If you connect everything the right way and take all the necessary precautions, there is little to worry about.

Two main dangers commonly associated with jump-starting a car are damaging delicate components in the electrical system and blowing up the battery. These situations can result from crossing the positive and negative cables or shorting them out by touching the positive and negative leads together.

When you use a jump box, the basic method of connecting it to the dead battery is the same as when you use jumper cables:

1. Connect the positive jump box cable to the positive terminal on the battery.

2. Connect the negative jump box cable to the engine block or another good ground location.

3. Set the jump box in a stable location in the engine compartment or on the ground if possible, where it won't become detached, fall, or interfere with the engine pulleys or fan.

4. Attempt to start the car.

5. Carefully disconnect the negative jump box cable and secure it to the jump box.

6. Carefully disconnect the positive jump box cable and secure it to the jump box.

Is It Dangerous to Jump-Start a Car With a Jump Box?

The major sources of danger when you jump-start a car apply whether you use another car or a jump box as the source of power. The first is that the dead battery may have explosive gas leaking out of it. The second is that you can damage the vehicle's electrical system if you hook the jump box up backward, and the third is that the jumper cables or jump box must be routed or set in a safe location.

While it's true that a certain level of risk is involved in jump-starting a car, you can minimize it to almost nothing if you follow the correct procedures.

When Jump-Starting Is a Bad Idea

There are a few instances where jump-starting is a bad idea. For example, many hybrid vehicles have a 12-volt auxiliary battery that can be jump-started if it goes dead, but attempting to use this low-capacity battery to provide a jump-start to someone else is a bad idea.

The problem is that such a small battery may end up completely drained after providing a jump-start, which could leave you stranded. So while most hybrids can be jump-started, think twice before offering one to someone else.

There is another potential jump-starting issue that's associated with vehicles that have batteries that are difficult to access. Some of these vehicles have a remote positive terminal for charging and jump-starting the battery, and others require you to do some work to access the battery.

In cases where a remote terminal isn't available, it's typically a bad idea and potentially unsafe to jump the vehicle by using the positive terminal on the fuse box or any other connection that isn't the battery.

Portable Car Jump Starters

As far as portable car jump starters are concerned, they're perfectly safe with the one caveat that you still have to follow all the correct procedures. You still need to hook up a car jump starter in the correct order and in the right places. You can only use one to jump-start a traditional car battery or the auxiliary 12V battery in a hybrid, but not the high voltage batteries in a hybrid.

The Importance of Connecting Cables Correctly

It is possible for your battery to blow up if you use a car jump starter, which is why it's important to hook up the cables correctly. If your battery is accessible, hook up the positive jump starter cable to the positive battery terminal first. If the battery isn't accessible, look for a remote positive terminal.

With the positive cable securely connected, locate a clean, unpainted part of the car's body, frame, or engine that isn't close to moving parts like the fan or accessory belts or near the battery.

The main reason you don’t want to hook up a car jump starter directly to the negative battery terminal is that doing so can create sparks. If the battery isn't working due to having been overcharged or due to an internal fault, it may be full of flammable vapors, which can seep out even if the battery is sealed.

Sparks can ignite these vapors, which can cause the battery to explode. If this happens, you may be showered in acid and severely injured. Although this isn't common, it can cause serious injuries.

Short Cable Concerns

In some cases, jump boxes have cables that are so short you need to connect both of them directly to the battery. If your jump box is like this, it's important to ensure all the accessories, such as the lights and radio, are turned off and that the key isn't in the ignition.

When connecting both positive and negative cables to the battery, connect the positive first, and then carefully connect the negative. If possible, wear protective clothing and eye protection, and attempt to shield yourself from a potential explosion.

Using a Car Jump Starter With a Hybrid

If you drive a hybrid, it's typically safe to use a car jump starter or a regular jump-start on the auxiliary battery. These auxiliary batteries are nominally 12V, just like regular car batteries, but they're typically smaller.

The main danger associated with hybrids and jump-starting is that if you use the auxiliary battery in your hybrid to jump someone else's car, you may end up depleting it to the point where your vehicle won't start. It is safe to use a jump starter or portable power pack on that type of battery.

The other type of battery contained in most hybrids uses a different, much higher voltage than the 12V used by conventional cars and trucks. You can't jump-start the main batteries in your hybrid with a car jump starter or jumper cables and another car.

Issues With Difficult-to-Access Batteries

If you drive a regular gas or diesel vehicle with a battery that's difficult to access, it may or may not be safe to use a car jump starter. It's safe to use one if your vehicle has a remote positive terminal that's designed for charging and jump-starting, but you should never hook the positive clamp of your portable jump starter to the fuse box or anything else that isn't meant for that purpose.

In some cases, the only safe way to use a portable jump starter is to access the battery and connect directly to the positive terminal.

Depending on where the battery is located, it may be impossible to make connections to both the positive battery terminal and a clean, unpainted section of the body or frame. This can make it difficult to use a jump box if the included cables are short. In this situation, you need to use actual jumper cables or a jump starter with longer cables.