Depending on the car, the car’s ignition may have 4 modes – LOCK, ACCESSORY (ACC), ON, and START. I have used them over the years (somehow) without really knowing the basics of what they are and their effect on the battery if any.
In my case, it was the ACC mode – Not knowing what it stands for, does, and whether it is bad for the battery life?
Read on to find out more including its impact on battery life and what to do should the battery die when the ignition key is in ACC mode.
But first:
The ACC Mode and What it Does
Turning the ignition to the ACC position turns on the battery power to the car’s electric circuit to then run any electrical accessories usually the car stereo, the charging port, and connected accessories that are wired to this circuit
Do you want to listen to the radio, charge the laptop or phone without starting the car? Turn the ignition to the ACC position.
The benefit of using the ACC position instead of turning the ignition to the ON position is that the power drain is lower by as low as 10% in some cars!
Is it Bad to Leave the Car in Accessory (ACC) Mode?
Leaving the ignition switch in the ACC position drains the battery
Leaving the car ignition in the ACC position can drain the car battery flat but usually over time. The impact on the battery charge for short durations, 15- 30 minutes or longer may be insignificant in case of a large capacity, fully charged battery.
A weak or aging battery can fail from being deeply discharged when the car is left in the ACC position.
Will the ACC mode Kill the Battery?
Not necessarily. You can leave your car’s ignition in the ACC position and even run accessories like the car stereo system and be able to start the engine provided the car battery is fully charged and in good condition.
Leaving the ignition key in the ACC position can accelerate battery failure if the battery is weak or aged.
Keep the engine running the engine from time to time to keep the battery topped up and able to start the car when required.
Does the ACC Mode Use Gas?
Turning the ignition key to the ACC position in and of itself only uses and drains the battery power.
You may have to keep the engine running to keep the battery topped up which uses gas.
ACC vs ON vs START
When you turn the ignition to the ACC position, it is the electrical accessories connected to the car’s internal ACC wiring circuit that are powered.
These are lower power consumption electrical accessories like the radio, and any accessories plugged into the ACC power socket.
Turning the key to the START position starts the car engine.
How Long Can a Car Last in ACC Mode?
Unfortunately, there’s no one answer. There’re several variables at play, but as a guide, a fully charged 50 Ah car battery in good condition can be drained to 50% of its capacity in about 67 hours (about 3 days).
This is based on tests I run using a 2015 Toyota model 1.8 liter car.
It had a current drain of about 370 milliamps with the ignition turned to the ACC position.
Note, your results may be different depending on for instance whether there’re any accessories switched on such as the car stereo and others as they increase the current draw on the battery.
To avoid the risk of draining the battery flat, turn the ignition to the OFF position.
How Quickly the Battery Discharges – The Factors
How quickly the battery charge is drained depends on:
- the car’s battery capacity and the state of the charge. A fully charged, larger capacity battery (Ah) will last longer
- the accessories switched on in the car at that time. Switching the ignition to ON by itself drains the battery power. Should there be additional accessories switched on – the car radio, lights then the battery will take an even shorter time to run out.
- the battery’s condition. An older battery that’s lost its ability to hold charge will drain faster than a newer or older battery that has not lost its capacity and ability to hold charge!
Related Questions
What to Do if Car Battery Dies in ACC Mode?
Should the car battery die when the ignition is in ACC mode, check for:
- corrosion around the battery terminals,
- loose battery connections,
- or even a car battery that’s losing its capacity to hold charge.
Arrange to have the car battery tested at a reputable auto store. It could also be that the alternator is not able to charge the battery.
Closing Thoughts
When the ignition key is turned to the ACC mode, the accessories circuit is powered, and the car accessories are wired to the circuit and switched too.
There’s some current draw on the battery in ACC mode (albeit lower than when the ignition is in the ON position) so switch it off if not needed or keep the engine running.
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