How Long a Car Battery Lasts with the Radio On?

Listening to your favorite talk show or music on the radio or car’s sound system can be one great way to kill the boredom as you wait for a friend or partner.

There is always a risk that the radio can drain the car battery flat leaving you unable to start the engine if one is carried away.

So, how long can you safely have the radio playing before draining the car battery flat?

Does leaving the radio on kill the battery?

Read on for guidance on how long you can expect a car battery to last with the radio on, whether leaving the radio on can damage the battery, and for tips on how to stop the radio from draining the battery flat.

How Long a Car Battery Lasts with the Radio On?

Quick Answer. As a rough guide, you should be able to play a car stereo receiver single DIN with an LCD screen off a fully charged 40-55 Ah car battery for an estimated 1-3 hours or more without the battery voltage dropping significantly That the car is unable to start.

In reality, how long the car battery lasts depends on the size and power draw of the radio, the volume level it is played at, the state of charge of the battery, and the condition of the battery.

If the radio volume is set to maximum, the capacity of the battery (Ah) is lower or if the battery has lost its ability to hold charge then the battery will last for a shorter time.

Why the Car Radio May Be Draining the Battery Flat?

If the car radio is draining the car battery flat sooner than expected then there are a few things you can check:

#1. confirm that the radio is switched off when the car’s ignition is in the off position. Could the radio be wired wrongly such that when even when the ignition is off, power still flows to the radio?

You can check this by using a good-quality current meter.

Set your digital multimeter to read dc current and measure the current flowing from the battery when the ignition is in the off position.

Next, remove the fuse protecting the wiring to the radio. Should the current flowing drop then there is still current flowing to the radio even when the ignition key has been removed.

Note: A car radio has an ignition sense wire that should be connected to an ignition switched power source.

The radio may need to be programmed (in its settings – check user manual) whether to turn on or off with the ignition key only, turn on or off with both ignition key or power switch radio.

Fix: Consult the car radio owner manual to confirm that the radio wiring has been connected according to the wiring instructions and the required programming done.

#2. The car battery may be partially charged or losing its ability to hold charge. As batteries age, they tend to lose their capacity to hold charge.

So, even when fully charged, the battery voltage can drop quickly when an appliance is switched on.

You can test the battery capacity by taking it to an auto mechanic or test it yourself.

You can also conduct a quick test of available capacity by charging the battery fully and then measure how long the headlamps can light before dimming.

Depending on the reserve capacity of the battery, the runtime can be anywhere from 60 – 90 minutes.

If it is significantly lower say 30-45 minutes then there is a high chance that the battery has lost some of its capacity.

Does Leaving the Car Radio on Kill the Battery?

Yes, leaving the car radio on for an extended period can drain the battery flat. In some cases, depending on the condition of the battery, the battery may be permanently damaged.

How Much Battery Power a Car Radio Uses?

This really depends – for example, a car stereo head unit with an inbuilt 4 x 45 w amp can draw up to 10 A ( about 120 watts at full power) depending on the volume level selected.

The power draw of car radios varies from one model to another based on features, power output, and volume level.

Assuming a 5 amp draw as an example, the radio may be able to play for about 5 hours before running down a 55 Ah battery to 50% of its capacity. In reality, though, there are many variables at play that affect how long the battery lasts.

How to Listen to Radio without Draining the Battery Flat?

#1. Keep the Car Engine Running

You can keep the car engine running so that the battery is topped up by the alternator and therefore not at risk of the starter battery being drained flat.

You may be interested in this post: Does leaving the car engine running charge the car battery?

#2. Monitor the Car Battery Voltage

Use a cigarette lighter plugin voltmeter to conveniently monitor the battery voltage as the car radio is playing.

Run the engine to top up the battery voltage if it drops to about 12.45V. At 12V, the car battery is significantly discharged.

#3. Install an additional deep-cycle auxiliary battery with a battery isolator to supply power to the car radio or sound system.

This gives you peace of mind as the starter battery charge remains intact and is not in danger of being drained flat.

#4. For Hybrid vehicles, switch the car to READY mode

This way, the 12V car battery is constantly being replenished with charge from the larger hybrid battery.

Should the hybrid’s battery voltage drop to a low level, the car will start the internal combustion vehicle to charge the hybrid battery.

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Final Word

You should be able to play a car stereo receiver, single DIN with an LCD screen off a fully charged 40-55 Ah car battery for an estimated 1-3 hours or more without the battery draining flat.

Actual run time depends on many variables such as the sound level it is played at, its power consumption (watts), battery capacity (Ah), and the state of charge of the battery.

If the battery is in good condition but is still being run down, it may be that it has been wired wrongly. Refer to the radio’s owner manual and check that it is wired as described in the manual and accordingly programmed.

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