Leaving the car radio on can drain your battery, but how long would it take before it dies completely?
If you’ve parked your car and left the radio running, it will use the charge remaining in its battery while the alternator is not charging it. So the battery’s charge will slowly diminish until it can no longer support the radio running. If you accidentally leave it on for a long period or overnight, you’ll want to know how long the battery can last.
If the car battery is new, it may last up to 8 hours with the radio on if it’s a standard flooded lead-acid battery. Otherwise, it may last from 4 to 6 hours, but it will drain sooner if you also have other accessories connected. The exact time will depend on the power draw and more factors, including initial charge, battery condition, ambient temperature, and the alternator.
I’ve also given a few tips to prolong the time the battery can give in case you’re listening to the radio without the engine on intentionally.
How Long a Car Battery Can Survive
Leaving the car radio on will no doubt slowly drain the battery, but how long can it survive?
When using a standard (flooded lead-acid) car battery, the car battery can last up to 8 hours if you leave the radio on. But it can drain sooner if you have a weak or old battery or the radio is connected to a subwoofer and amplifier.
In these cases, it may only last 4 to 6 years unless the battery is very weak or old, in which case it could easily drain much sooner, perhaps within a couple of hours.
So, a car battery can get drained completely if you accidentally leave the radio on overnight, but it may not drain that much if only left for a few hours.
If it’s not accidental, and you’re listening to the radio with the engine off, you should start it and let it run for at least 5 minutes every half an hour. This will help to keep the battery charged.
But exactly how long your car battery can endure such a situation, i.e., leaving the radio on accidentally for a long time or overnight, depends ultimately on these factors:
- How charged is the battery initially
- How weak or old is the battery is
- The radio’s power consumption, including other accessories connected to it
Before looking at how long the battery can last further, let me explain how the car battery works and how leaving the radio on affects it.
How Leaving the Radio On Affects the Battery
One analogy to explain how a battery works in a vehicle is to consider it a wound-up spring. [DeHays, 2015]
Two things can cause the spring to unwind: cranking the engine and using an accessory while the engine is off, such as leaving the radio or lights on. The spring only gets a chance to wind up again while the engine is running, and it does this quickly when you drive. The alternator takes care of that to provide all the electrical power needed.
Leaving the radio on for a long time can potentially leave the spring unwound so much that it cannot crank the car. If it doesn’t unwind this much and allows you to crank the engine, you can wind it again; otherwise, it cannot.
Factors that Affect How Long the Battery Has
Let’s look at the factors that affect how long a battery has in more detail.
To reiterate, the main factors are:
- Initial charge
- Battery’s age and condition
- Radio’s power consumption
I will also consider other factors you might not be aware of.
Initial Charge
The more the initial charge, the longer the battery will last with the radio on; the less the initial charge, the shorter the time it will give.
Battery’s Age, Condition, and Type
A typical car battery lasts no more than 3 to 5 years.
But it can weaken and die sooner if you don’t take good care of it. Therefore, the battery’s condition is an important factor in how long the battery can last with the radio on.
A new battery can provide more power than an old or weak battery. As you may expect, it can support a radio left on for longer. A new and healthy lithium-ion battery could last 24 hours, but it is not commonly used in a non-electric car.
Depending on the battery’s age and condition, a battery used for a while may last only 40-80% as long. Protect your car battery from extreme temperatures and overcharging.
An old or weak battery will hardly last long and die quickly.
Radio’s Power Consumption
The radio’s power consumption will determine how much it will drain the battery or the discharge rate.
The consumption depends on the type of radio and whether it has any accessories attached to it, such as a speaker, subwoofer, or amplifier. Such extras usually consume a lot of power. A high-end audio system in your car will draw much more power than a simple or electrically efficient radio operating alone. How high the volume is will also make a negative impact.
A typical car radio, when operating alone, will draw around 3 to 5 amps with the volume at a reasonable level. Adding an amplifier may increase the current draw to around 10 to 30 amps, making a 2- to 10-fold difference.
A radio’s power consumption also depends on which frequency band you listen to. The FM and satellite bands drain the battery quicker than the AM band.
Was it only the radio? If you leave more accessories on than just the radio and other things connected directly to it, you can expect the car’s battery to die quickly.
So, suppose you’re listening to the radio with the engine off intentionally. In that case, you can make the battery last a little longer by listening to an AM station, disconnecting attachments, and turning off all other accessories.
Other Factors
The ambient temperature and the alternator are other factors affecting how long a battery will last.
A car battery will discharge faster in very cold weather. So, listening to the radio with the engine off on a very cold day is not a good idea. Leaving it on accidentally can make your battery die and leave you unable to crank the engine. The risk is less on a warmer day.
The alternator, which charges the battery while the engine runs, can affect how quickly the battery can be recharged. If the alternator is weak or faulty, it may leave the battery undercharged. Consequently, a battery that is not fully charged will be unable to last long with the radio on.
Can the Battery Die?
Having read this far, you will know that the battery can die very quickly if any one or more of the following applies:
- Initial charge – The battery’s initial charge is low.
- Age – The battery is old.
- Weakness – The battery is weak.
- Battery type – You’re using a standard flooded lead-acid battery instead of an AGM or lithium-ion one.
- Engine – If the engine is off throughout.
- Band – If it’s an FM or satellite band or station.
- Extras – If you have a speaker, subwoofer, or amplifier connected to it.
- Accessories – If you have other car accessories on simultaneously.
- Temperature – If it’s a cold day or night.
- Alternator – If the alternator is weak or faulty.
The more these factors apply, the less time the battery will have to keep the radio going. Once the battery is completely dead, there will be no more power to keep it going, so it will stop.
Tips for Prolonging the Time a Car Battery Can Give
To listen to the car radio with the engine off intentionally, you will want to ensure the battery can last as long as possible without draining too much.
Here’s what you can do (try to do as many of them as possible):
- Battery – Ensure the battery is fully charged before turning the engine off. Replace a weak or old battery regularly or install a lithium-ion one.
- Engine – Run the engine for at least 5 minutes every half an hour to help keep the battery charged.
- Alternator – Maintain the alternator to ensure it’s always in good working condition.
- Parking – Try to park in a warm spot (but it should not be too hot either).
- Radio – Listen to an AM station, keep the volume low, and disconnect all attachments.
- Other accessories – Turn off all other accessories in the car.
- Source – Play the audio content from your smartphone or another device so that the car radio uses minimal power. Use the aux port or Bluetooth if possible.
- Power – Use a solar charger to trickle-charge the battery.
- Accessory Mode – Switch to the Accessory Mode if you have the option in your car. It will consume less power and make the battery last longer.
Suppose you’re interested in learning more about listening to a car radio without draining the battery in detail. In that case, I recommend you read this article: “How to Listen to the Radio without Draining the Car Battery.”
References
Larry DeHays. The Car Care World, How to Get Your Car Fixed Without Being Taken for a Ride. AuthorHouse. 2015. Retrieved from https://www.google.com.pk/books/edition/The_Car_Care_World/_LjrBgAAQBAJ?hl=en&gbpv=0
Video References
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