How Long It Will Take Before Car Battery Dies With Radio On? (Explained)

Have you ever wondered how long it will take before car battery dies with radio on?

Look no more. We´ve got you covered.

Whether you are tailgating, camping, or just gazing from your parked vehicle; it is always a more pleasant experience with a radio blasting or just playing in the background.

If need be, you can even use your car radio running of the car battery to stay either informed or entertained when for some reason you are without power.

The real question is not can you run radio from a car battery. You can, it’s plain and obvious because cars rarely come without a radio and some type of stereo system.

The question is how long it will take before car battery dies with radio on?

According to experts, when using a standard car battery, the radio will run for about 8 hours before the car battery runs out. However, if your car has an amplifier and a subwoofer, the radio’s listening time before the battery is discharged is reduced to about 6 hours.

Table of Contents

How Long Can A Radio Run On Car Battery?

How long you can listen to music or radio shows on your car radio using only a car battery depends on two things, the power draw of your radio and battery capacity.

Taking into account the current draw in amps of radio makes it convenient to determine the maximum listening time as the car battery is expressed in ampere-hours.

So, to calculate it all you have to do is to divide the car battery capacity with the current rating of the radio.

Older car radios without amplifiers would typically draw anywhere between 0.25 amps to around 1.5 amps. With the car battery’s capacity typically being around 40Ah, it would last for many hours with volume at some conversational level.

On the other hand, modern car stereo systems, because they have amplifiers, even when they are idle with the volume turned to 0, can draw from 1.6 amps and up.

And with the volume blaring at maximum can draw above 10 amps. At some normal volume levels, modern systems will draw around 5 amps of current.

With a battery of 40 amp-hours, this gives maximum listening time before the battery dies between 4 and 8 hours.

In case that your vehicle has an aftermarket audio system, with an amplifier and subwoofer, current draw can easily go up to 25 amps, which proportionally decreases the time it can run on the car battery.

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Can Speaker Rating Be Used For Calculating Power Consumption?

When it comes to car audio systems, and audio systems in general, one of the most common numbers related to their output you can find is their RMS rating in watts.

Just presuming that dividing this number with 12 volts car battery voltage will give you their amp rating is a huge error. Especially when it is related to sound systems with amplifiers.

The first problem is in the nature of what RMS is. It is not the maximum power draw of the speakers, but actually an average power the speaker can sustain over a longer period of time without the heat buildup in coils distorting the sound.

It does correlate with the maximum loudness of the system, but power draw is influenced by many other things too.

One of the reasons for this is the inefficiency of amplifiers.

Amplifiers Efficiency

Currently on the market most common classes of amplifiers for audio systems fall in either class AB or D.

These classes are divided by nominal efficiency of amplifying the sound waves, and for class AB range from 25% to 75%, while for class C it ranges from 85% to 95%.

These inefficiencies always mean increased power consumption when using them for in-car audio systems.

But also can make calculating expected power consumption practically impossible if the exact level of efficiency is not known.

And amplifier manufacturers rarely do print them on their units or in manuals.

Instead, you may find a maximum power consumption on amplifiers, which can be a misleading figure.

Maximum Power Consumption Of An Amplifier

On the backside of an amplifier, you will find printed a number stating the maximum power consumption.

This is a number that is related to power consumption when an amplifier is producing the maximum power output in worse conditions possible, such as with 1 or 2 ohms speakers.

Because most of the available car speakers have resistances of 4, 6, or 8 ohms; actual power consumption when outputting the maximum power is two to four times below this number.

But, the realistic power consumption will actually be even lower because of two things.

First, you will very likely not use the sound system at maximum volume and maximum power output, as it cannot sustain it for a longer time without clipping and other distortions of the sound.

And also due to the nature of soundwaves, which have hills and valleys, it will draw even less power.

In the end, it is realistic to expect that an amplified car sound system draws around 10% of the rated maximum power consumption of the amplifier.

Does Radio’s Power Consumption Change With Songs Being Played?

What songs you are playing does in fact impact how much power is your audio system drawing. To understand how and why you need to understand how speakers produce sound.

All speakers have magnets, coils, and a diaphragm. Magnets and coils produce a magnetic field of variable strength and other characteristics which in turn cause the diaphragm to vibrate and thus produce the sound.

To produce a sound of some frequency, the diaphragm needs to vibrate at the same frequency.

And it takes power to make it vibrate. The higher the frequency is expected to be produced, the more power is needed.

Because of this, when playing music with a lot of mid and high tones, your audio system draws more amps and consumes more watts than when playing music that is dominated by low-frequency sounds.

Should I Use Radio When Engine Is Off?

In general terms, you can use your radio when your car engine is off, but it is not the best practice. Car batteries are designed to deliver huge amounts of current during the short periods of time needed to start the engine.

They are not intended to be drained over a long period of time.

One of the problems is relatively very thin lead elements used for storing electricity in the form of chemical bonds.

All batteries have a certain number of recharge cycles they can withstand before they are not able to be recharged anymore.

For many battery technologies, this means that if you always deplete them to 0% you should expect the rated number of times to recharge them. While if you always deplete them to 50% of the capacity, you should expect twice the number of rated charging cycles.

When it comes to car batteries, deeper discharges, under 50% capacity level, actually damage it and severely decrease the life span.

So, the best practice is to avoid using any device running from a car battery for a much longer time than it needs to deplete half of the battery’s capacity. When it comes to radio and car’s audio systems, it means that the best practice is to not use them longer than 3-4 hours with the engine off.

There are many situations when you may want to turn on the radio in your car. But sometimes you might want to still keep the engine off, either to preserve the gas or for a multitude of other reasons.

But a question for how long you can keep the radio on before the car battery dies remains.

The answer is simply complicated. It depends on the exact power draw of your whole audio system, and if it has an amplifier and subwoofer, its power draw can increase multiple times.

Some general time for somewhat usual sound systems ranges between 4 and 8 hours.

But if you are conscious of the health of your car’s battery, you will not listen to the radio with the engine off for longer than 3 to 4 hours on a daily basis.

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How Long Can You Listen To The Radio With The Car Off

On average you can listen to the radio for 2 to 3 hours without running the car battery down.

How Long Can I Leave My Car In Accessory Mode

You can expect to leave your car for around 30 to 45 minutes in accessory mode. However, the newest car turns off the accessory mode after 20 minutes to avoid draining the battery; this is on a timer or the vehicle analyzes how much electricity is consumed.

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