How Many Ways Will My Car Battery Die? And How To Handle It

At the time of this writing, the United States and many other areas are ‘opening up’ economically.  With Covid-19 shutting down many avenues of entertainment people are looking for things to do that meet new acceptable social guidelines. 

Enter the drive-in movie theater.  Not that long ago it was considered a novelty and on the endangered list, but now drive-in’s are making a comeback. 

But there is a whole generation of people who are naive as to how to attend a drive-in properly.  They don’t know what to bring or how to set up their car. One of the most common questions is ‘will my car battery die at the drive-in move’? 

Yes, it will, but only if you let it.  A drive-in movie is usually broadcast on an FM frequency; which your car radio conveniently carries.  But running your car’s electronics while not running the car will most definitely kill your battery.

There are ways around this, however, the most common solution to this is to bring your own portable radio/boombox.  These are battery-powered and run independently of your car’s power supply.
  
One that comes highly recommended is the Pyle Portable Speaker from Amazon.   It has a strong FM receiver, perfect for a drive-in movie, and it is also Bluetooth, making it versatile enough for camping, picnics, and other outdoor activities. For more information on how to set up your car so that your battery doesn’t die check out my article 13 drive-in movie car setup ideas.

We have all been there before, haven’t we?  Running around putting stuff in our trunks, taking it out.  Then there is that one time that the trunk doesn’t close all the way and the trunk light stays on.  Will a car battery die from leaving the trunk open?

The short answer is ‘YES’ leaving the trunk open with the light on will eventually drain your battery.  Leaving any light on will eventually drain your battery.  Now let’s qualify this answer a bit because there are many several factors at play here.

What is the age of your battery?  If you have a fairly new battery then you may have several days before it is completely dead.  However, if it is an old battery you may only have several hours until it is dead.  Personally, I have left the dome light on inside my truck all night.  I had just replaced my battery though (this article has that story and some other very useful information), and when I went to start my truck the next morning, it fired right up.  So battery age has a lot to do with whether or not it will survive the trunk being left open.

Another factor to consider is your vehicle’s own built-in safety features.  Do the interior lights turn themselves off after a period of time? If so, the trunk light will more than likely go out.
  
So, to summarize; yes eventually leaving the trunk open could cause your battery to die. But this could take from several hours to several days, depending on the health of your car battery.  Try to give it a good slam next time, so you don’t have to worry about it.

What does the ‘ACC’ on the car ignition even mean?  The ACC is one of the four positions on the car’s ignition switch positions, and it stands for ‘ACCESSORY’.   That makes sense, right?  So, accessories would include anything from your radio to your phone, to the lights in the car.

Will your car battery die if it is left in the ‘ACC’ mode?  Yes, your car battery will die if it is left in the accessory mode.  Yes, the accessory mode is drawing less power but it is still drawing power from the battery; which will eventually run out of power. Or not have enough power to start the car again.

Now there are a number of factors that are involved here.  Again the age and condition of your battery are of primary importance.  Any aftermarket additions you have made to the stereo or speakers will affect the power drain. Even the type of light bulbs that may be installed.
The ‘ACC’ feature is very useful for short periods of time.  Just be cautious not to overextend your car batteries’ capabilities.

Again, Yes, it will.  The radio is drawing power from the battery to the transmitter and the speakers.  Eventually, your battery will die.
In theory, it should take hours for your car battery to die listening to the radio. An easy way to avoid this is by occasionally starting your vehicle and letting it run for a few minutes. This will give your battery a little bit of charge to keep going.

Surprisingly, this is a very complicated question and requires some math to answer.  I will try to summarize it for you.  But first, according to Time magazine, the short answer to this question is ‘YES’, charging your phone could possibly kill your car battery. However, the likelihood of that happening is not great. 

Let me try to explain.  Once again, the health and age of your battery come into play here; an older battery will be more adversely affected than a newer car battery.  The following math will show that it is very difficult for your phone charger to drain your battery.

First, we need to understand a car battery’s capacity, which varies, so all the numbers you are about to see are ballpark. Warning, Math ahead.  Let’s assume that a car battery is anywhere between 40-60 Amps/ hour (Ah), this will give 720 watts of stored energy more or less.  Now also keep in mind that your car battery is a 12-volt battery (12v-that’s important for the math). Alright, now to the math:

Car Battery Wattage: Let’s assume a 50 Ah battery at 12 v
50Ah * 12V / 2=  300 Watts per hour (Wh)
Cell Phone Battery: Cell phone batteries are typically 3.7 v with a frequency of 3500 mAh (or 3.5Ah).
3.5 Ah * 3.7 v =  13 Watts per Hour (Wh)

So based on the above formula you could charge your cell phone about 23 times before you drain your car battery.

Most likely you will have access to a continuous power source before you need to recharge your phone 23 times.  And like I said these numbers vary, some phone batteries require more voltage and some car batteries have less power.  

Let’s just run a comparison to try to make this a little bit clearer.  Your headlights consume about 40-60 watts per hour. Using the math above, that means that, a car’s headlights will drain a battery in about 5 or 6 hours.

To sum this mess up.  If you have a healthy battery and your phone is cold dead, you should still be able to charge it up without killing your battery.  Just be mindful of any other accessories that are running, because they will be drawing battery power, too.

The answer depends on what kind of car you have.  According to my research for most cars, the answer is ‘NO’, your air conditioner will not kill your car battery.  However, if you drive an EV vehicle the air conditioner will reduce the battery’s capacity.

In a standard gasoline engine, the AC is run off of electricity produced by the alternator. So your vehicle must be running in order for the AC to even work.  The battery has nothing to do with powering the air conditioner unit so it will be fine.

However, if your vehicle is off, and the key is in the ‘ACC’ position you can still turn the air conditioner fan on.  Having the fan running will drain your car battery if the car is not on and the alternator not producing electricity.  

This question has taken on new meaning here in 2020.  With the US and many other countries amid a global pandemic, our cars are sitting more than ever.  My van has had the same tank of gas for the last four weeks.  But we are talking about batteries here.

According to cars.com, your car battery is the most susceptible to degradation of all car parts from extended sitting.  Again, it depends on the age and health of your battery; and again ‘YES’ allowing your car to sit for extended periods will drain your car battery.  

Several computer systems are still running even though you are not.  It’s pretty awesome that your car knows your playlist and connects to your phone, but you know what?  That Bluetooth is still running.  That Bluetooth is still draining your battery! The same can be said of your car’s clock, alarm system, and any other myriads of systems in your vehicle.

One other thing that affects your battery adversely is extreme cold.  Disconnecting your battery and storing inside may be the thing to do if your car battery will be exposed to extremely cold temperatures.  When you are ready to use it, you can charge it first and then install it in your vehicle.  Check out my article Best Car Battery For Winter over here to find helpful tips on which battery may be best for your car.

There are a few ways to avoid having your battery die while it is sitting for extended periods.  One way is to start your car and let it run for 10-20 minutes each week.  Allowing your car to run will give the alternator a chance to recharge your battery.

Another way is to use a battery tender, this will feed your car battery a small charge to keep it from dying.  I use this on a battery that I have and it works wonders.  My vehicle will sit for two to three weeks at a time and when I go to start it up; there are no issues.