Can Leaving the Car Interior Light Cause the Battery to Die?

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A drained car battery that leaves the car unable to start in the morning can be a source of frustration and panic, particularly when you are in a rush.

Whereas there are several possible reasons why the car battery may be drained, one of the more common causes is when you leave the interior lights switched on.

It may also be that a door or trunk has not been closed properly triggering the interior light to come on and stay lit (in cars without an automatic switch-off of lights when the ignition is off).

It is normal to have concerns about the battery when it is drained, for example, whether the battery can be revived or if it has been permanently damaged.

So, this post provides some helpful insight on the likely impact of the interior lights on the car battery when left switched on, if the drained battery can be revived, how long you can expect the lights to work before the battery dies, and lastly provides some suggestions on how you may be able to protect your car from battery drain.

Quick answer. Leaving the car’s interior lights on is one of the factors that can cause battery drain but not the only one.

The extent to which a battery is affected when the lights are left on depends on the battery condition and state of charge of the battery among other factors.

Read on for how long you can expect the car interior light to last before the battery is drained and tips to protect your car battery from being drained.

Will the Car Battery Die when interior lights are left on Overnight?

An older battery nearing its end will likely have its life cut short when it is drained by leaving the cabin lights on.

A fully charged battery condition on the other hand will likely be more resilient though it is generally advisable to avoid deep discharges in general as they affect its lifespan if they happen several times.

Will the Car battery recharge?

If the battery is newer, fully charged, and still in good condition, you’ll likely be able to revive it by charging it.

Keep in mind though that frequent deep discharges tend to affect how long the battery lasts.

Ultimately, whether the battery lasts or dies depends on a number of variables such as the battery condition, battery capacity, and whether filament or LED bulbs are used in interior lighting.

A newer, fully charged car battery, with LED interior lights, is likely to suffer little or no damage compared to an older, partially charged battery in a car that uses filament bulbs for interior lighting.

Modern cars’ interior lights have the auto-switch off function

Note: Modern and newer cars’ interior lights may automatically be switched off after a preset time when the ignition key has been removed to prevent deep and damaging discharge of the battery.

Why Interior Light May Be Drawing a Battery Flat?

While it is possible for an interior light to drain the car battery flat when left on for an extended period, it may also be a sign of an underlying problem with the car.

#1. Is the car alternator still able to charge the battery fully? If the car battery is only partially discharged then the car battery will drain faster with the interior light left on.

You can do a quick test of whether the alternator still works by measuring its output voltage with the battery connected.

If the digital multimeter reading is between 13.5- 14.5V then the alternator is most likely working well.

As this test is not always conclusive, you can still arrange for the alternator to be tested at an auto repair shop if the battery shows signs of low voltage.

You may also be interested in: Why the Car Alternator Output Voltage may be Low (How to Check)

#2. The car battery might be aging and losing its capacity to hold charge. An aging or damaged battery’s charge level drops quickly even when it has been fully charged.

A quick test you can do is to charge 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.

Additionally, have the car battery tested at an auto repair shop.

All in all, yes the drain may be from the interior light but the car may have some underlying faults with the alternator or car battery that need to be fixed.

How Much Power (watts) an Interior Car Light Consumes?

If the car uses the dome light bulbs then the power draw may be as much as 8 watts (estimated).

Newer LED modules consume significantly less power and can draw 4 watts or less.

Keep in mind that the power drawn by the car’s interior lighting depends on the number of lights switched on and so can add up if, for example, you have the interior dome, map reading, and trunk lights switched on instead of one or two.

How Long a Car Battery Lasts with the Interior Light On

A 4-watt interior light can burn for about 3.5 days and only draw a fully charged 55 Ah car battery to 50% of its capacity.

An 8-watt dome light can last for about 1.7 hours (estimated) with the same capacity.

So it depends on the power consumption of the lights used, battery capacity, state of charge, and how many lights are switched on.

Tips to Prevent the Interior Lights from Draining the Car Battery Flat

Here are some tips that can minimize the likelihood of the car battery being drained flat by the interior light(s).

#1. Is the car using dome light bulbs for its interior lighting? Consider replacing with LED light modules.

They are brighter and consume significantly less power (50% or more) than the filament light bulbs.

#2. Are the dome interior lights set to permanently on mode or auto (usually) the middle position switch? If the light selector switch position is set to ON, then the interior light will stay on draining the battery even when the ignition key is removed.

#3. You can also consider installing a battery saver or low voltage disconnect switch that protects the car battery from damaging deep discharges.

Always be Prepared

Lastly, it never hurts to be prepared, always keep a set of jumper cables or a portable jumpstarter pack in the car to get you back on the road in the event that the battery is drained flat.

Final Word

While in newer modern cars, leaving the interior lights on is less likely to result in battery drain because of the automatic switch-off features inbuilt, it still happens in the older cars.

Unfortunately, if your battery is drained too often, it can result in permanent damage that requires an investment in a new battery.

To protect the battery from being drained, consider replacing the interior light bulbs with the LED bulbs and make sure the light settings are set to automatically switch off when the ignition key is removed (older cars).

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