How Long Will a 12V Battery Run a Radio? (Explained)

How Long Will a 12V Battery Run a Radio

Have you ever wondered how long will a 12V battery run a radio? Look no more. We´ve got you covered.

The 12 volts batteries come in many shapes and sizes. The best known and most widely used are the automotive lead-acid batteries and their “cousins” deep cycle batteries.

Whether you are camping, living off-the-grid, or just plain lost power due to weather; you may wish to know for how long you can run a radio or audio system on it.

So, how long will a 12V battery run a radio? With modern car audio systems and the most common car battery capacity of around 40Ah, you can run a radio for around 4 to 8 hours, but because car batteries are very sensitive to deep discharges, you should limit using the radio with the engine off to 2-3 hours.

Deep cycle batteries can provide a longer running time than proportionally to their larger capacity.

How long the battery will run the radio will also depends on the battery capacity and the power draw of your radio.

How Much Power A Radio Consumes

When talking about car audio systems in relation to battery consumption, the most convenient is to use the amperage.

The battery capacity is always expressed in ampere-hours, so the ampere rating of the sound system allows for a quick calculation of running times.

To calculate a ballpark value all you need is to divide the capacity of the battery by the amperage of the radio.

Older car radios that didn’t have amplifiers used to draw between 0.25 and 1.5 amps.

Newer OEM car audio systems usually draw from 1.6 amps, due to the inefficiency of the amplifiers they would draw this much even when idle with the volume turned to 0, but not radio itself.

When volume is on maximum they can draw more than 10 amps, but the average current they need is around 5 amps.

Aftermarket custom sound systems with proper stand-alone amplifiers and subwoofers can draw much higher current, and depending on the exact configuration, they can reach currents above 25 amps, even when the most efficient class D amplifiers are used.

If a class AB amplifier is used, due to its inefficiency, the current needed for the same audio system can be 2-3 times higher.

Battery Types And Their Capacities

There are several types of batteries that can be used for powering a radio, such as the 23A type which used for various radio-operated gadgets and their controllers, NiCd, and lithium battery packs for various portable devices, and so on.

But the types you are most likely interested in are the automotive and deep cycle batteries.

Automotive Batteries

These batteries are almost exclusively a variation of lead-acid technology. Very often, car batteries are considered by laymen as the only type of them.

But in reality, car batteries are just one of the form factors of automotive batteries, though they are the most common ones.

Various types of these batteries differ in intended use, from light personal vehicles to heavy-duty truck batteries.

Most common car batteries have a capacity of 40 to 45Ah, which will provide you with 4 to 8 hours of radio run time, depending on the actual current it needs.

In case that you need to power an aftermarket audio system, you should be aware that the battery capacity doesn’t scale proportionally to current. The higher the current is, the shorter the running time will be.

“In other words, if an audio system pulls 5 amps, it could run up to 8 hours on a 40Ah battery. But a 10 amps audio system will not be able to run for 4 hours on the same battery.”

Instead, it very likely will be able to run for around 2 hours.

When it comes to automotive batteries there is another concern you should be aware of. They are designed to deliver high currents over short periods of time measured in seconds, which is why they are also called start-up batteries.

And are not very good at delivering low currents over long periods of time, measured in hours.

To preserve their lifespan, it is best to not drain them below 50% of their capacity without recharging them.

In practice, this means that you shouldn’t very often have the radio on for longer than 2-3 hours without the engine running.

In case that you discharge the car battery to a level below 50% on a regular basis, its lifespan will be greatly reduced.

Deep Cycle Batteries

Deep cycle batteries the most general terms are lead-acid batteries similar to the automotive type, but with thicker lead sheets which allows them to be more appropriate for providing constant currents over longer periods of time.

While there are some newer types of deep cycle batteries, such as LiFe and lithium polymer, the most common type are acid-lead batteries.

When it comes to getting the most of the lifespan from a deep cycle battery, the best practice is to always discharge it to a level under 50% of their capacity, before recharging, and to even try to go as low as 0%.

Shallow discharges do shorten their lifespan and decrease the maximum number of charging cycles.

Read also: How Long Can I Run a TV Off a Deep Cycle Battery? (Easy Explained)

For example, if a battery has around 500 charging cycles life span when discharging to 0% percent, when always discharging to 90% it will not have 5,000 charging cycles lifespan but closer to 3,200.

While common-sense advice is to not discharge them below 50%, it flies in the face of the science. These batteries are not just capable of withstanding being fully discharged but are actually intended.

When it comes to how long you can run a radio of them, it depends on their capacity. Most common are 105Ah capacity deep cycle batteries, but their capacity can be even higher than 400Ah.

These nominal capacities ratings are based on 20 hours of running cycle and with higher discharging currents their capacity does decrease.

A 105Ah capacity means that over a 20 hours period the battery can supply a constant current of 5.25 amps.

If you are using an audio system that draws exactly 5 amps doesn’t mean that you will be able to run it for 21 hours, but closer to 23 hours.

At the same time, an aftermarket audio system that draws 10 amps will not be able to run for 10.5 hours from the same battery, but more likely just a few minutes longer than 8 hours.

When it comes to running a radio or audio system from a 12V battery, the most common situations are the car audio system powered by an automotive battery, in case of a passenger vehicle, or by a deep cycle battery.

How long you can run it depends on how much that audio system is power-hungry and the capacity of the battery.


Mike Gilmour

Hi, I'm Mike, co-founder, and editor of RV and Playa. My passion is traveling (with my RV) and enjoying the day at the beach (Playa)! Well, I originally created this blog as a way to share what I've learned by experimenting with the RV lifestyle, and I want to help others develop in life through new skills and opportunities.

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