Adding a Second Car Battery for High Performance Audio

Tokyo Auto Salon 2015
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Question: Can High Performance Car Audio Benefit From a Second Battery?

I want to add a second battery or something so that I have more power to run my high performance audio equipment, but I’m not sure how to go about it. What kind of options do I have, and what do you think is the best way to add extra backup power for a really high end car audio setup like mine?

Powering Performance Car Audio Systems

If you want to add some extra juice to run your performance audio equipment, you have two basic options. The first option is to ditch your OEM battery for the biggest, highest capacity battery that will fit in the available space. This is the easiest solution, and it’s typically good enough for most situations.

The other option is to replace your single battery with matched brand new batteries or add a deep cycle backup. This is more complicated, but it can potentially give you even more reserve amperage, and it has the added advantage of allowing you to install the second battery close to your amplifier.

Of course, it's also important to remember that there are situations where a stiffening cap or a high output alternator will be a better idea than an extra battery. Adding a second battery is a good idea if you want to be able to run your car audio system longer when the engine is off, but it won't do you any good when the engine is actually running.

High Performance Batteries for High Performance Audio

Since you’re in the market for more power for your performance audio equipment, what you’re really looking for is more reserve capacity. Batteries all have a number of different ratings, but two of the important ones are cranking amps and reserve capacity.

Cranking amps refers to how much amperage the battery can provide at one time under a heavy load, i.e. when you are cranking the engine, and reserve capacity, usually given in ampere hours, refers to what the battery can deliver over an extended amount of time. That means you’re looking for a high performance battery that offers a lot of reserve capacity.

Depending on what car you’re driving, you may or may not have some extra space to work with where your battery is concerned. As long as a replacement battery physically fits into the allotted space, and you can safely strap it down, it’s perfectly fine to replace an OEM battery with an aftermarket one that has a significantly larger reserve capacity.

If you have space for a bigger battery, then that's the simplest option. Replacing a small OEM battery with a larger capacity one is basically just a matter of pulling the old battery, putting the new one in, and hooking up the battery cables. It doesn't get any easier than that.

Second Batteries for High Performance Audio

The other way to add extra reserve battery capacity is to actually add a second battery. In this case, you’re typically going to get the best results by ditching your existing battery and putting in two, brand new, matched batteries. They don’t have to be the same group as the original battery, but they should be the same group (and same production date) as each other. This is essentially just to ensure that one battery doesn’t end up getting overworked, which can lead to a shortened life expectancy.

If you’re installing matched batteries, one should go right where the OEM battery was, and the other needs to be wired in parallel. You can install the second battery in the passenger compartment or the trunk, although you need to take precautions if you install it in the passenger compartment.

You can also keep your existing battery and add a deep cycle or marine battery. This option is a little different, because you have to wire it so that you can isolate each battery from the electrical system. The idea is to use the original battery when you're driving, and the bigger deep cycle battery when you're parked. This has the added advantage that you won't ever accidentally leave yourself with too little power to start your car back up.

Whether you swap out for a bigger battery or install a second one, finding a spot with the right horizontal dimensions isn't enough. If the new battery is tall enough to ground out on the hood, you'll have to look for other options.

The Problem With Extra Battery Capacity

Whether you install a high capacity battery, or a second battery wired in parallel, it’s important to remember that you’ll only really see a benefit when the engine is off. That’s when the extra capacity really comes in handy. Whenever the engine is running, the extra battery is just an extra load as far as the alternator is concerned, which can overstress an old (or underpowered) unit.

Depending on the precise issue that you’re trying to address, you may actually be better off with a car audio capacitor than an extra battery. Although stiffening caps typically aren’t the best solution for anyone who actually enters car audio competitions, they can often solve minor problems like headlights that dim during especially loud or bass-heavy music.