Tech

Do You Need a Second Battery for Car Audio?

Installing a different battery for the stereo probably won’t help

Unless you want to listen to music with the engine off, adding a dedicated car stereo battery won’t do you any good and can actually hurt. This may seem counterintuitive, but the reasoning is simple.

Your car battery has only one purpose: to provide enough power to start the engine. After the engine is running and the alternator is running, the battery acts as the load. If you add a second battery it will act as a second load while the engine is running as the alternator will charge both batteries.

When the battery is low

One battery is good, so two must be better, right? This is the case in some cases. When the engine is not running, any accessories you turn on are powered directly from the battery. That’s why if you accidentally leave your headlights on at night, you’ll come back with a dead battery. If you add a larger battery or a second battery, you’ll have extra backup power.

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The main reason to add a second battery to a car or truck is if you need accessories when the engine isn’t running. If you’re in a camper, that’s a good example. You can go away for a weekend or more without running the engine, which will drain your battery very quickly. Adding a second battery allows you to spend more time without running the engine and charging it.

If you have a habit of parking and using the sound system for hours on end, you may need a second battery. In all other cases it may not solve the problem you are trying to solve.

Listening to the car radio with the engine off

Whether you have a powerful car audio system that you want to show off, or you go camping and want to power multiple devices, your battery is limited in how much you can use it. The battery that came with your car will only run your stereo for about an hour with the engine off.

If you want to estimate how long your stereo can run with the engine off, or know how much spare capacity you should be looking for in a second car stereo battery, here’s the formula:

10 x RC / load = runtime

In this formula, RC stands for Reserve Capacity, a number in amp-hours that indicates how much charge the battery has available when fully charged. The charging portion of the equation refers to the continuous charging power, measured in watts, produced by a car audio system or other electronic device.

Let’s say your car audio system has a load of 300 watts and your battery has a spare capacity of 70. This results in the following calculations:

10 x 70 / 300 = 2.33 hours

If your car audio system has aftermarket amplifiers and correspondingly higher loads, the amount of time you can use the stereo with the engine off will be reduced. Adding a second battery will increase the time.

In many cases, the battery will indicate reserve capacity in minutes rather than amp-hours. If your battery says it has 70 minutes of reserve capacity, that means a 25 amp load will take 70 minutes to discharge the battery below 10.5 volts. In practice, the actual number will vary depending on ambient temperature and battery condition.

Car Audio Batteries: Excessive Charge!

Adding a second battery can cause problems as it charges extra every time the engine runs. In other words, an electrical load is anything that draws current. From headlights to car stereos, your accessories and batteries are a burden.

When the battery powers the starter motor to start the engine, it draws power from the alternator. This is why the charging system is difficult to drive with a dead battery: the alternator is not designed to work.

When you add a second battery to the car, add another bucket to fill the alternator. If the second battery is deeply discharged, it can overload the alternator. So if you’re having issues like dimming your headlights when turning up the music volume, adding a second battery will make the problem worse.

Content

Do You Need a Second Battery for Car Audio?

It may not help to install another battery for your stereo

Unless you want to listen to music with your engine off, adding a dedicated car audio battery isn’t going to do you any good—and it may actually hurt. That might seem counterintuitive, but the reasoning is simple.

The battery in your car is there to serve one purpose: to provide enough amperage to start the engine. After the engine is running, and the alternator is spinning, the battery acts as a load. If you add a second battery, it’s going to act as a second load when the engine is running because the alternator keeps both batteries charged.

When One Battery Just Isn’t Enough

One battery is good, so two must be better, right? There are a few situations where that’s the case. When the engine isn’t running, any accessories you turn on pull current directly from the battery. That’s why you’ll come back to a dead battery if you accidentally leave the headlights on overnight. If you add a bigger battery or a second battery, you end up with extra reserve power.

Westend61 / Getty Images

The main reason to add a second battery to a car or truck is if you need to use your accessories when the engine isn’t running. If you take your vehicle camping, that’s a good example. You may be out for a weekend, or longer, without running the engine, and that can drain the battery quickly. If you add a second battery, you can go longer without running the engine and charging it back up.

If you make a habit of parking your car and using the audio system for hours on end, a second battery might be in order. In all other cases, it’s probably not going to solve the problem you’re trying to deal with.

Listening to Your Car Stereo With the Engine Turned Off

Whether you have a high-performance car audio system that you want to show off, or you’re going camping and want to power several devices, the battery has a limited capacity to work with. The battery your car came with may only be able to run your stereo for an hour or so with the engine off.

If you want to estimate how long you can run your stereo with the engine off, or figure out how much reserve capacity to look for in a second car audio battery, here’s the formula:

10 x RC / Load = Operating Time

In this formula, RC stands for reserve capacity, which is a number, in amp-hours, that indicates how much power the battery has available on a full charge. The Load part of the equation refers to the sustained load power, measured in watts, pulled by your car audio system or other electronic devices.

Let’s say that your car audio system represents a 300-watt load and the battery has a reserve capacity of 70. This would result in the following calculation:

10 x 70 / 300 = 2.33 hours

If your car audio system has an aftermarket amplifier and a correspondingly higher load, the amount of time you’ll be able to run your stereo with the engine off will go down. If you add a second battery, the time will go up.

In many cases, a battery will show a reserve capacity in terms of minutes rather than amp hours. If your battery shows that it has a reserve capacity of 70 minutes, that means it will take 70 minutes for a 25 amp load to drain the battery below 10.5 volts. In reality, the real number will differ depending on the ambient temperature and the condition of the battery.

Car Audio Batteries: What a Load

Adding a second battery can cause problems because it acts as an additional load whenever the engine runs. In other terms, an electrical load is anything that draws current. Your accessories—from the headlights to your car stereo—are loads, and so is the battery.

While the battery provides current to the starter motor to get the engine going, it draws current from the alternator afterward. That’s why driving with a dead battery is hard on a charging system—alternators aren’t meant to be worked that hard.

When you add a second battery to your car, you’re adding another bucket for your alternator to fill. If the second battery is discharged to any great degree, it may overtax the alternator. So if you’re dealing with issues like dimming headlights when you turn up the music, adding a second battery can make the problem worse.

#Battery #Car #Audio

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