Car Battery Dead from Sitting? What you Need to Know

If a car has been sitting for a few days, even with a new battery installed, you may be unable to start it leaving you wondering what’s causing it.

Can a car battery go dead from sitting? If so, what can you do to avoid this?

To find out if this is possible and what you need to do to better protect your car’s battery, read on.

Can a Car Battery Die from Sitting?

Yes, a car battery can drain flat from sitting. How long it takes to drain depends on the age and health of the battery, its state of charge, and if there are any accessories drawing power from it even with the car ignition off.

A battery that has been in service for several years and is only partially charged will likely last a shorter time before draining than a new battery that is fully charged.

How Long a Car Battery Lasts

This depends on several variables. A fully charged battery in good condition should be able to last at least 1-2 weeks (estimate) or longer. Ultimately how long it lasts depends on the battery capacity (Ah), its charge level, and the current drain by the connected car accessories that remain on even with the car ignition off.

What Causes a Car Battery to Die

A battery that is sitting can still die because of the following:

1. Some car accessories continue to use battery power even when the ignition is off. Car accessories that remain connected to the battery such as a car alarm, and the onboard car computer continue drawing the battery power.

While the draw may appear minimal (up to 50 mA), over several days and weeks, this draw adds up substantially. Assuming an amp draw of 50mA, over a period of 2 weeks, this works out to 16.8Ah, nearly 40% the capacity of a 40Ah battery!

2. Batteries lose their capacity to hold charge over time. As batteries age, they tend to lose their capacity and ability to store charge and drain faster. Don’t expect the car battery to perform as well as a new one after 3-4 years of regular use.

There is nothing you can do to fix this when it kicks in except to replace the battery.

3. Car batteries self-discharge. It is normal for a car battery to gradually lose charge even when no accessory is connected to it. To counter this, the battery needs to be topped up regularly.

4. A car battery can fail permanently if not stored properly. A car battery needs to be stored in a cool, dry place and maintained at full charge.

How long a car battery sits before being charged?

You should either connect it to a battery maintainer such that its voltage is maintained above 12.4V. Or, charge it fully then disconnect it from the car battery terminals to prevent current draw by car accessories but periodically top up its charge every 3-6 months so that it is always above 12.4 V.

Do not let a car dead battery sit. Charge it fully and always keep its charge level up to avoid premature failure of the battery.

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Is it Normal for a Car Battery to Die after Sitting for a Week

You can have a healthy battery drain flat in under a week. How fast a battery lasts when sitting depends on several variables:

  • it’s capacity (Ah),
  • level of charge,
  • age, and
  • the current drawn by the connected accessories when the car’s ignition is turned off.

If it drains in 1-2 days then there is an issue. There are several possible lines of investigation you can follow but definitely check for a parasitic current draw by car accessories, a failing alternator or battery, or loose or weakly connected car batteries.

Tips to Prevent a Car Battery from Dying

To prevent the car battery from dying, connect it to a car battery maintainer to counter any parasitic current draw and self-discharge.

You can also disconnect it completely from the car battery terminals, charge it fully, and periodically monitor its voltage always keeping it above 12.4V.

Will a Car Battery Go Dead Sitting on Concrete?

This is not an issue with newer batteries that have the hard plastic casing which acts as a good insulator. It is okay to store your car battery on a concrete flow.

Closing Thoughts

Yes, a car battery can go dead from sitting. How long it takes depends on the health, age of the battery, if it is fully charged and the current drawn by connected car accessories.

Keep the car battery fully charged and watch out for a parasitic current draw. Replace your car battery when it starts losing its ability to hold charge. Arrange the battery to be tested at a reputable auto parts store.

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