Does Leaving Keys In the Ignition Drain Battery? (Guide)

It depends on the type of ignition system you have. With older cars, the ones without electronic key fobs, leaving the key in the ignition did nothing but prove you have a bad memory. As long as the key is not turned on, then you won’t drain the battery. Having a newer car may be a different story.

There are key situations where you can drain your battery if you leave the key in the ignition all night. The electronic key fobs communicate with the electronic system of your vehicle and when left in the ignition, that drains a lot of power.

To learn more about this situation, just continue to read our article. It explores this topic so you have the best information possible and hopefully reminds you to remove the keys when you get out of your vehicle.

Does Leaving The Keys in The Ignition Drain The Battery?


It can do this but it will depend on how you leave the keys in your car and what type of ignition system your car has. Old-fashion keys may not do anything unless you leave the ignition in the on or ACC position.

When you do that, the circuit is complete and some electronic parts will function. Without the motor running to recharge the battery, then the battery will lose its power.

Leaving the key off all night, should not do anything to the battery. But if you have one of the more modern electronic ignition systems where a key fob communicates with the car’s electronic system, then you will have a problem with whether the ignition is on or off.

Then with the detection systems some cars have, the system detects that the key is in the ignition and starts to prepare components for ignition. When this happens you can lose power or damage some other component.

Leaving The Key in The Ignition With The Car Off


Again, it depends on the situation and the position the key is in. With newer cars that run off computerized components, it may not matter if the key is off or in the on position. There will always be some power drain.

How much power drain depends on the position of the key. Then, it may take a long time before the battery is drained completely. Most people may only leave the keys in the ignition overnight. That means that very little power may be drained from the battery.

But with those new key fobs that like talking to the electronic system, the power drain may be higher. It will all depend on the make and model of your car and the type of system it has under the hood.

In today’s world, you shouldn’t forget to take the keys out as there have been alarms that remind you the key is still in the ignition.

Why Does Leaving Keys in The Ignition Drain The Battery?


The key is a vital component in the ignition system. Without it, the circuit cannot be completed and no power can travel through the electronic systems. Once the key is inserted into the ignition, the circuit is completed and power may be sent to pre-ignition components.

That is with the normal key. Sometimes it takes turning the key to the on or ACC position before the circuit is complete. If that is the case, then you won’t have to worry about a dead battery in the morning.

But with these new fobs carmakers are using, it is a different story. Those fobs communicate with the electronic system regardless if the key is turned on or off. That communication uses electricity thus your battery will lose power overnight.

How much it will lose depends on the car, etc., and how long it has been left in the ignition. Plus, it will depend on how old your battery is as well.

Left Keys in Ignition Battery Dead


The term ‘dead’ is a bit subjective here. Batteries are considered dead when they reach a certain percentage of power and they will not start. You have to be careful not to have the battery go that low. You may not be able to recharge it.

But if the engine sounds like it is trying to turn over, then you can still connect a battery charger to get the power back. Some people have said that you can recharge a dead battery through the hot terminal of the alternator or the starter.

That may or may not work depending on how your car was made. Essentially, if the engine won’t turn over and it is due to lack of battery power, replacing or recharging the battery are your only options.

How Long Will a Car Battery Last With The Ignition On?


This will depend on many factors. One of the factors will be the age of your battery. While normally, you may have up to two weeks to remove the key before the battery loses power but that is not guaranteed.

If the battery is old, it may take only a day for it to lose its power. The next factor will be how much power is being drained at the time. Different car model years have different components that take power at different rates.

Your battery’s power loss will depend on how much power is being used by these different components. Detection systems will use power first. Then the fob may be communicating with the electronic system so that will take a certain amount of power.

The power loss depends on the electronic system in your vehicle.

Some Final Words

It may be a sign of getting older but leaving your keys in your car is not a good idea anymore. There are too many upgrades to an engine system that uses electronic power and leaving the cars in the ignition is not a time saver anymore.

Hopefully, your vehicle lets you know when you leave your keys in the ignition before you get out of the seat. It used to be that way.

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