- by Bryan Veldboom - updated on 9/28/2021
At one point or another, most of us have experienced the frustration of a dead car battery. Ordinarily when that happens, you would just jump start the dead vehicle, however, some vehicles have their batteries mounted in an unusual location, such as under the back seat. So, how do you jump start a vehicle with an inaccessible negative battery terminal?
The answer to this depends on which vehicle has the inaccessible terminal. If you can’t access the negative terminal on the dead car, it’s not a problem. In fact, when jump starting a vehicle, experts recommend connecting the negative clamp to a metal ground instead of the negative terminal of the dead battery. Use an unpainted metal part of the engine block.
If you’re trying to use a vehicle with an inaccessible negative terminal as the donor vehicle, that’s a different matter entirely. These vehicles are not designed for that type of access and should not be used to jump start other cars or trucks. If you have one of these vehicles, but still feel like playing the good Samaritan, we suggest picking up a jump pack. Jump packs are portable batteries that enable you to jump start a vehicle without the need for a second vehicle. For more information, read our blog article entitled, "How Do You Jump a Car with a Portable Power Pack?"
Before you begin, you need to make sure that the donor vehicle’s battery has the same voltage as that of the dead battery. That means if the dead car has a 12-volt battery, the donor car must have a 12-volt battery too. If you’re not sure of your battery’s voltage, you can find this information in your driver’s manual.
You’ll also want to take a look at the battery itself before attempting to jump it to make sure there’s no damage present. Never attempt to jump a battery that has leaks, cracks or corrosion present. Likewise, you should also avoid jumping a battery in which the electrolyte inside it has frozen or evaporated. If you have a flooded battery, you can verify this by checking the battery’s cells. Use a plastic putty knife or screwdriver to pry the lids off the top of the battery’s cells and then use a flashlight to look inside.
The electrolyte is too low if any part of the plates is exposed to the air. If this is the case, you’ll need to top off the cell with distilled water before attempting to jump it. Add just enough so that the plates are covered. If you notice any ice in the battery’s cells, you have a frozen battery on your hands and you should not attempt to jump start it.
Please note that if you have an AGM battery or another type that is labeled as “Maintenance free,” you should not attempt to open it.
You’ll also want to be sure that you’re using a high quality set of jumper cables free of any tears or cuts in the wiring. Read more about what to look for in a set of jumper cables, or pick up a new pair of jumper cables from Batteries Plus.
When using jumper cables, start by connecting the positive (red) clamp to the positive terminal of the dead battery. Then, connect the positive (red) clamp to the positive terminal of the donor car’s battery. Next, connect the negative (black) clamp to the negative terminal of the donor car. Finally, connect the remaining negative (black) clamp to the engine block or other metal ground. For more in-depth instructions visit the "How to Jump Start a Car" page on the Batteries Plus website.
Are you constantly having to jump start your vehicle? It could be an issue with your battery. Why not stop by your nearest Batteries Plus and have it tested for free? If it’s time for a replacement, our experts can help you find the right vehicle battery for your needs. We also install batteries in most model vehicles too. Plus, you can pick up new headlight bulbs, auto fuses, windshield wiper blades and other essentials at our Automotive Center.