How Long Can a Battery Last on Accessory Mode?

Lock key ignition switch accessory mode

Keeping your car in accessory mode might be just the thing you need while waiting around. Some people want to use it for hours on end while they wait for a friend or stalk their ex-girlfriend (please don’t do this). As such, it’s a common question to wonder how long a battery can last on accessory mode.

Your car’s battery can last a long time on accessory mode. With few, low-consumption electronics, good outside temperatures, and a healthy battery, your car can easily last overnight. In unfavorable conditions, it might just last a few hours or less. It all depends on your specific situation.

In this article, I’m going to talk all about the accessory mode. I’ll teach you what it is, what it does, why it’s so great, and specifically how long you can expect your battery to last when you’re in this mode.

The 4 Positions of Your Car’s Ignition

When you look at the slot that your car keys slide into, you’ll notice that there are four positions. Accessory mode is just one of the four. All of them, in order, are:

  • The first is “OFF” or “LOCK”
  • The second is “ACC” which stands for “accessory”
  • The third is “ON”
  • The fourth engages your starter and cranks your engine

Clearly, I’ll be talking about the second position a lot in this piece. Just to make things clear, let me briefly explain the other three.

Close up of a car key ignition switch with key in accessory mode

OFF/ LOCK Position

This position explains itself. There is no electricity flowing from your battery to any components in your car. Nothing will work within your vehicle with the exception of some dome lights that automatically turn on when you open your doors.

Unless the car is in “PARK,” you won’t be able to move outside of this position.

ON Position

The “ON” position will turn on components within your car. In addition, all of the safety lights on your dash will probably come on momentarily at this point.

Engine Crank Position

The fourth position is also called the “START” position. By turning your key beyond the “ON” position and holding it there long enough, your car will start. If you have trouble starting your car, take a look at this guide.

Once cranked, the engine will turn over and the vehicle will start running. At this point, you can drive away.

What Is Battery Accessory Mode?

The second position is “accessory”, but what does this mean? It’s a position where some electricity will flow from your car’s battery, but the vehicle will not be operational.

In other words, you won’t be able to drive your car around but you’ll be able to listen to the radio and charge your phone inside the car. This draw comes directly from the battery.

The Problem with Accessory Mode

Since the engine isn’t running, this leads to a big problem: the alternator isn’t running.

As a reminder, the alternator is the piece of your engine that recharges your battery as you drive along. It will slightly recharge when you’re idling, but it starts to seriously recharge your battery when there’s a load on the engine — more specifically when your car is driving around.

One of the reasons why people suggest against idling overnight is because the alternator can’t properly recharge your battery, and the same story is true here.

Car-starting-system

Think of it this way: your car battery is a lot like your phone’s battery. Your phone needs to be recharged regularly to keep working. When it’s dead, it won’t work until it’s charged again.

With your car battery, it will ultimately die if the alternator isn’t recharging it. Once dead, it will only run again after a jump start and the alternator gets to run.

How to Go to Battery Accessory Mode

Getting into “accessory mode” is pretty straightforward. Simply turn your key clockwise until you land on the marked position.

Keep in mind, you need to turn it much less than you typically do to start the car. If you can hear your engine running, then you’re not in accessory mode.

The Purpose of Accessory Mode

Why do people even use this “mode?” It’s all a matter of convenience. If you’re going to be sitting in your car for a while, the accessory mode will help kill some of the boredom.

More specifically, you can play music, use overhead lights, and charge your phone with a USB wire in your car.

This could be used in an emergency where you’re stuck and really need to charge your phone. Alternatively, you can simply use it when you’re waiting for a friend to come to your car or a kid to finish up their sports practice.

The only real alternative to using accessory mode in your car is to keep it idling. As you probably know, idling isn’t good for the environment and will waste the gas in your car.

How Long Can a Battery Last on Accessory Mode?

Now it’s time to answer the question on everyone’s minds: how long can a battery last on accessory mode?

The simple answer is that it really depends on a few things:

  • Outside temperature
  • How many electronic components are being powered
  • What types of components are being powered
  • The life of your battery
Charger plug phone on car

I always suggest routinely checking the life of your battery before thinking about leaving it idling or running in “accessory mode” for a long time.

So, if it’s very cold, you have a lot of high-consumption components running, and your battery life is low, then your car won’t last long on accessory mode.

On the flip side, if it’s a reasonable temperature, your components are low-consumption and you’re only using a few, and your battery is new and healthy, then your car could probably last overnight on accessory mode with no problem.

If you want an exact number, you’re probably looking at a number less than 10 hours. With poor conditions and a nearly dead battery, maybe closer to 4 hours.

Is it Bad to Keep a Car on Accessory Mode?

There’s nothing super bad about keeping your car on accessory mode, even if you do it routinely. It’s a built-in feature for your car, so it’s not going to act like a self-destruct button.

In a lot of cases, it’s actually a lot better for your car to use accessory mode rather than idling the vehicle (to achieve the same results).

How to Run Accessory Mode on a Push-to-Start Car

What if your car doesn’t have a key slot? You can still access accessory mode.

With a push-to-start button, it’s as simple as removing your foot from the brake when starting your vehicle. In other words, keep both feet on the ground in front of your seat and press the start button on your car.

At that point, your radio should turn on and different electrical components will start working. If it’s not working, then you might have a dead battery.

Pushing the engine start stop button of a car

Things to Avoid in Accessory Mode

Obviously, the number one way to prolong your time spent in accessory mode is to minimize the strain on your car’s battery. There are a few big players to avoid when you use accessory mode:

  • Aftermarket subwoofers – I’m a big music guy, so I’m a fan of buying the best car speakers. This leads a lot of owners to install a big, beefy subwoofer that they throw in the trunk. While this installation might be great for incredible basslines in music, it’s a quick way to fry your car in accessory mode. The amount of power required to power these big guys is unbelievable.
  • Moving your seat with power controls – Power seats are driven from your car’s battery. Don’t believe me? Try moving your seats with the power controls when your car is turned off or your battery is dead.
  • Rolling up and down windows repeatedly – Another component that takes an unnecessary toll on your battery is your windows. Rolling them up and down repeatedly might seem innocent enough, but the impact can add up.
  • A/C & Heat – Even though the A/C compressor isn’t on since the engine is off, the fact that the climate control, fans and other electronics are on, it can quickly drain the battery.
  • Your GPS – Plug-in navigation systems will also drain some of your battery. While the drain isn’t huge, it’s an unnecessary device to have plugged in while you’re sitting stationary in accessory mode.

Conclusion

At this point, you should have some confidence in your car’s accessory mode. You know how to maximize the time you’ll get in this mode, and you know some of the great perks of using accessory mode. For more car guides, check out the rest of my blog. Take a look at some important car care products that you should pick up.

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Ernest Martynyuk

An automotive enthusiast who's been tinkering with vehicles since I was 15-years old. Repairing automotive electronics has been my main job for over a decade now and have a passion for everything technical regarding cars.

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