Does ACC Drain Your Car Battery?(No! But)

Does ACC Drain Your Car Battery?

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Does ACC Drain Your Car Battery?

An Engine Start/Stop button is famous for helping you start and stop your engine. However, there is another largely ignored use of this button,activating ACC (Accessory mode).

This mode enables you to use your car’s electrical resources, including audio system, navigation, and power windows, without the need to start the engine.

Not many people appreciate the difference between activating the Accessory Mode and starting the engine.

While you might be worried that ACC might drain the battery, your worries are not justified unless you leave it activated for very long periods.

Also, if you run Accessories after ACC is activated, you need to worry about the battery as it will be drained.

Normally, ACC will not drain your car battery. But the electronic devices that you use will drain your battery if your car is not running.

Here, insert the ignition key and rotate it once as this is the second position in the ignition switch.

If you are in an automatic transmission, you will need to press the start or stop button without braking, press the button three times, and then press your radio volume knob once.

You don’t need to confuse this procedure with starting the car as you need to start and stop it.

Does A Car Battery Charge While Driving?

Yes, a car’s charging system is boosted by driving, especially when you rev the engine.

It will take a maximum of 30 minutes to bring your battery from flat to a full charge.

However, this time might be increased if you are running electrical in the car.

You might need to consider switching electrical, including radio, the heating system, and headlights for best results.

Your car will charge better and faster when being driven as opposed to when idling. The alternator charges your car as it provides electricity to charge your battery.

The production of this electricity is dependent on the status of the engine, whether or not it is running.

But how much of that charge goes to the battery depends on other factors, as I have just insinuated.

For instance, all of that electricity will not go to the battery if you run high-power demanding gadgets in your car. 

Your battery provides electricity to the starter to turn over your engine, enabling it to fire up and start running.

When it starts running, your car’s engine will keep running as long it’s in good shape and has enough gasoline.

Connected to a serpentine belt, it will turn it, enabling it to power your car accessories and provide them with electricity to function. 

The alternator is one of such accessories. In turn, the alternator will charge the battery so that your car will start the next time you stop.

Your alternator’s electromagnet is driven by the serpentine belt(Amazon Link), enabling it to put out about 14-15 volts as your engine runs.

Does Revving The Engine Charge The Battery?

Yes, your car battery will charge even when the engine revs.There is a relationship between revving the engine and battery charging in your car.

Well, technically, your battery will not only charge when you rev your engine, but it will also charge faster, as seen earlier.

However, this is more evident when your battery is in a significantly discharged state.

Manufacturers design cars to ensure the battery maintains its charge throughout.

Does ACC Drain Your Car Battery?

When your car is idling, Lead-acid batteries will only need the amps from the alternator unless the battery is in a deficient state of charge.

When the battery receives increased amperage than an idle alternator. Alternator amperage increases when the engine is revved, contributing to faster charging.

In this condition, the operation of the alternator is hastened and, in return, aids in faster charging.

To understand this better, a car’s charging system generates current from the coordination of other components.

The crankshaft connected to the engine turns the motor, and revving the crankshaft increases the turning speed.

This moves the alternator belt, which links to the rotor. When this rotates, the alternator will generate a current which will pass through the voltage regulator.

The system’s interconnectedness explains why revving your engine results in an increased amount of current produced by the alternator.

Consequently, more current will be channeled to the battery for faster charging.

Will Charging My Phone While In ACC Drain Battery?

You might realize that your phone is low on power and needs some recharging when in your car.

If your vehicle isn’t running and you plug in your phone to charge, you might wonder, will my phone drain my car battery? All dread a dead car battery.

We know that today’s smartphone batteries have integrated lithium polymer technology. The battery capacity is in mAh (milliamp hours).

For instance, the iPhone 6 has a capacity of 1,810 mAh. As you use your phone, the charge will run down, and you will need to recharge it.

Considering our iPhone 6 battery, if your car has a 100 Ah battery, the phone will draw about 2% of the charge.

This might be too little or enough to drain your car battery.

For instance, you might want to think of the unlikely but possible scenario that your car might only hold a 2% resting charge, meaning that your phone will quickly kill it.

However, leaving your phone plugged in your car doesn’t mean your battery will be drained in a more practical world.

But then, you will need to have a car model that does not require your keys to be in the ignition to power the cigarette port.

Newer models allow that, but the older models need the ignition key to open the ACC.

Does A Car Battery Charge Faster If You Drive Faster?

Yes, driving faster turns your engine more quickly. And if the engine turns faster, the alternator will also turn faster.

This makes it easy to direct all of the alternator’s power to recharge the battery.

Indeed, you can either drive faster or rev your engine after your car starts to optimize on the charging.

However, you can drive to your destination as the battery will charge anyway.

After your engine’s alternator is engaged above idle speed, its full output potential is reached.

If you drive faster, it means that your engine will cause the alternator to run faster, consequently engaging it beyond idle speed in a consistent manner.

However, as you rev your engine, it is advisable to avoid pushing it beyond 2000 RPM. Drive for about half an hour to avoid needing to jump-start your car again.

Remember that you can hurt your vehicle by revving the engine. Do not rev the engine when it is cold or when in neutral.

Should I Disconnect My Car Battery Before Removing Radio?

Yes, for the sake of safety. By default, most car electronics have their power supply from contractors and relays driven by the car’s computer or ECU.

When you turn the car key on the ON position, these relays will always close. Consequently, the radio is only powered in the ON position or ACC position.

This should not be confused with other electronic systems like car security, WiFi for keyless entry, alarm systems, and some ECUs.  

For most modern cars, onboard computers will remain on all the time.

Therefore I strongly recommend that you disconnect your battery if you must work with these systems I mentioned.

As you can see, your radio is not among these, but you can disconnect the battery. Either way, it should not hurt, but read on.

An aspect of the car needs to be understood well when working on your car electrical; your car does not have a true ground as it’s separated from this by the tires.

This means that its grounding comes from the battery’s negative terminal that connects to the car’s body.

As you might know, there are capacitors in the car’s electrical systems that might remain charged. This static potential will quickly kill car electronics.

Consequently, with the car battery in-circuit, you will have static potential, which might damage the electrical in your car.

One of the most delicate electrical in the car is the computer ECU. This can be damaged as you remove your radio.

The bottom line is this; it’s best to disconnect your battery before removing your radio.

Can A Completely Dead Battery Be Recharged?

A majority of car owners face a faulty battery sometime in their car ownership lifetime. A faulty battery will fail to bring your car to life.

But can you recharge a completely dead battery? While it is not easy to fix a completely dead battery, it’s not impossible to recharge it.

The easiest way to recharge a completely dead battery is to jump-start your car and run your engine for some time.

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When a battery is completely dead, it means that its voltage falls below a functional amount.

Normally, this can be anything below 12 volts as car batteries run 12 or more volts. A battery can die due to a faulty charging system or faulty battery.

Leaving your electronic gadgets running for long without running your engine might also kill your battery.

But if you drive around if your battery has a good amount of voltage, this might be fixed.

Is It Better To Charge A Battery At 2 Amps Or 10 Amps?

Recharging a car battery can take many forms. There is a myriad of charges at which you might want to charge your car battery.

The greatest concern among car owners is whether to use 2 amp or 10 amp. The amperage at which you charge your car battery is hinged on the charge time.

While your choice of either using a 2 amp or 10 amp charger will predict the charge time, your battery capacity and type will also play a big role in charge time calculation.

Car batteries do better if slow charged. Lower amps will be better when charging a car battery, making two amps better than ten amps.

But this will depend on the other factors I mentioned. For instance, do you have more time than this will require?

All in all, anything beyond 20 amps is not recommended for car batteries.

Can You Disconnect The Negative Terminal?

Yes, the negative is what you want to disconnect as a safety precaution when working on your car.

But you need to ensure that it doesn’t touch any part of your vehicle’s body.

Being on the ground will ensure that you stay safe from any shock when working on your car’s engines and other parts.

To disconnect it, turn off your vehicle and remove the key from the ignition. Get to the battery under the hood by securing the hood with its stand.

Look for the back cable that attaches to the battery by a clamp. Squeeze, open and remove this from the battery terminal.

You will then be safe to work on the car.

Will Car Battery Drain If Negative Cable Disconnected?

Yes, a car battery will self-discharge if the negative cable is disconnected.

However, this will be at a rate of about 5% per month. This is better than leaving it hooked, only to discharge at a rate of 20% per week!

The best way to leave your car battery if you are not using your car for an extended time is to hook it up to a charger.

Why disconnecting the negative terminal will minimize the loss of charge on your battery; it is not enough to stop your battery from losing charge.

Every battery undergoes a process known as self-discharge.

As long as your battery is not connected to a smart charge and “float charge” selected, it will self-discharge as the chemical reverts from “charged” to “discharged” status.

This is why your battery will still discharge, even with the negative disconnected.

Why Do You Have Connect The Positive Terminal First?

When connecting your car battery, you start with the positive. After this, hook your negative to the body, anywhere.

Consequently, if there is a spark or arc, your battery will be safe from damage. Also, this will prevent it from blowing on you!  


Normally, ACC will not drain your car battery. But the electronic devices that you use will drain your battery if your car is not running.

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