Second Battery Installation Locations and Procedures

Where and how to install a second car battery

car battery cutaway illustration

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Some vehicles have space for adding a second battery under the hood, but they are the exception rather than the rule. Most vehicles that do have space for an auxiliary battery are either trucks or SUVs, so if you drive anything smaller, you’ll typically have to come up with some other solution. There are safe ways to install an auxiliary battery inside the trunk or passenger compartment of a car, but the best solution will depend on exactly why you need a second battery.

Second Battery Placement for High-End Audio

If you’re adding a second battery to provide extra reserve power for a high-end audio system when the engine isn’t running, then you’ll typically want to install it as close to your amplifier as possible, whether that’s in the passenger compartment or the trunk. In either case, you are correct to be concerned about the potential safety implications of installing a battery anywhere other than the engine compartment. In addition to the hazards associated with leaked (or spilled) battery acid and fumes, batteries can explode due to overcharging, internal faults, and other factors.

It’s absolutely vital to install a battery inside a sturdy, leak-proof box if it’s going to be placed either inside the passenger compartment or the trunk of a passenger vehicle. In nautical applications, there are actually regulations that specify exactly what type of box must be used to contain lead-acid batteries, but in cars and trucks, you’re free to use cases made out of either plastic or metal.

In any case, the battery box that you choose should have a water-tight base to contain any electrolyte that leaks or spills out a removable cover that provides access for maintenance, and pass-throughs for the battery cables. It’s also important to properly secure the battery box by bolting or strapping it down to prevent it from shifting around whenever your vehicle is in motion.

Second Battery Placement for Other Applications

If you want to add a second battery for any other reason, such as camping or tailgating, then the installation location isn’t important. Unlike high-end audio systems, where placing the battery close to the amplifier allows the amp to draw power with less electrical resistance, a second battery that is simply meant to provide reserve power to an inverter or other components can be located anywhere. The trunk is typically going to be the most convenient location, but this is mainly a matter of personal choice.

Regardless of why you’re installing a second battery, it’s still important to place it inside a sturdy battery box for the reasons outlined above. It’s also a good idea to use the heaviest gauge battery cables that you can.

Second Battery Alternatives

Although a second battery can provide extra reserve capacity to power various electronics when you’re tailgating, camping, or enjoying other outdoor activities in your car, there are a handful of easier alternatives that you may want to consider. A portable generator can typically provide more power than a battery, and there are a lot of great, compact units out there. Some portable generators even have built-in battery charging hardware, and unlike batteries, you can always buy (or carry around) extra gas for a generator.

Another option you may want to consider is sometimes referred to as a “jump box” because it’s essentially a gel-pack battery with built-in jumper cables. Although these devices were originally designed to provide emergency jump starts without the need for another vehicle, most of them are also available with built-in 12-volt accessory outlets, and some of them even have built-in inverters.

Of course, like all batteries, jump boxes have limitations. For instance, a typical jump box with a built-in inverter might be able to power a small laptop or portable video game system for five hours or so, but at that point, it won’t have enough juice to perform its intended function until you recharge it.