Here is a very short answer to why your battery keeps dying over and over again ….
Your Car Battery Keeps Dying Because There Is a Parasitic Draw, Issues With The Charging System, or An Internal Issue In The Battery Itself.
In this article I’ll show you how to find out the cause of your battery draw and some common fixes you can do yourself!
We Will Cover…
Why Do Batteries Die?
Batteries become weaker over time. The stress of multiple charge cycles weakens the active material in the conductor plates. This happens until the battery can’t move current anymore.
Remember, a battery does not die while you are driving because the alternator is continually sending the battery amperage that recharges the plates inside of the battery case.
The weaker a battery gets the less “capacity” it has to hold a charge. This is why a parasitic draw can cause real issues especially if the battery is older.
Changing a battery is not all that hard (although it has gotten much more technical over the years.)
The real issues start when you install a new battery just to find out it’s dead the next day.
Anyone at this point knows something is draining that battery … The real question is WHAT?
What Is a Battery Draw?
A parasitic battery draw (or drain) is simply an electrical load that the battery is trying to feed while the vehicle is completely off.
Depending on how much amperage this draw is sapping, it can leave even a new battery dead in a short timeframe.
Be sure all the doors, trunk, glovebox are shut tight and other accessories are off before chasing a battery draw. A simple charger plugged into a cigarette lighter port can throw off your diagnoses.
Before we dive in I want to clear up a few things here …
- I am targeting a battery that is still in good condition and does take a charge, this article is simply about BATTERY DRAW.
- If your car battery keeps dying and it fails to accept a charge you need to have it load tested and most likely replaced.
- This article is intended for the person that is a little handy, if that’s not you no worries, there is still a lot to learn here.
“Scoots Garage is reader supported, this article contains affiliate links. Purchasing through these links doesn’t affect your cost and helps support this site so we can keep creating content.”
How To Find Out Why Your Battery Keeps Dying Using a Multimeter
The easiest way to check battery draw is to remove the negative battery terminal and hook an amp meter inline.
One lead to the negative battery cable, and one to the negative battery lug. This will measure the amperage being drawn from the battery while the car is sitting.
You are simply putting an amp meter inline with the ground.
This is how to determine how much power is being pulled from the battery while the vehicle is off and parked.
Some things to keep in mind
- Newer cars that use a CAN network require 20 – 30 Minutes to “go to sleep” In other words the network is still communicating and will draw the battery until the network is commanded off.
- Depending on the meter there is a good chance you can blow the internal fuse of your meter if you are not careful.
- Newer vehicles draw quite a bit of amperage when the battery is first hooked up. This can damage your meter if it’s not set up right.
The above example is the fastest way to check for battery draw. Hooking up a meter inline will tell you if a draw on the battery is the issue and how much that draw actually is.
The meter I use and highly recommend is the Fluke 88, the fluke is an awesome meter that allows you to record the min and max draw overnight.
You can see exactly what the high and low points of battery draw are.
How Much Battery Draw?
Now that we know how to see exactly how much juice is being pulled from the battery the next question is …
“How much draw is too much?”
First and foremost, there we always be some parasitic draw on any vehicle. A rule of thumb is the newer cars tend to draw more than the older stuff.
Newer vehicles require much more amperage to keep all of the electronics working, even when parked there are modules talking to each other over the CAN (controller area network) until things go to sleep.
20 to 60 milliamps is a good place to be, on newer vehicles 80 to 100 milliamps is still ok if the vehicle is driven daily.
That is the higher point however, any higher and you may be wondering why your car battery keeps dying.
Here is the basic flow to determine why your battery keeps dying. I will explain each step further below.
- Hook up your multimeter inline and read battery draw after vehicle has sat for at least 20 minutes, (this allows newer vehicles CAN networks to shut down completely)
- Determine where you stand 20 to 60 milliamps? 100 to 600? If the draw is above 100 milliamps for an extended period we need to find the circuit responsible.
- While watching your meter pull one fuse out at a time and determine if the draw drops, this will isolate which components are on the circuit.
- Narrow the issue down and fix it!
The Step By Step Breakdown (Video)
The Vehicle Wake Up Issue
Using the multimeter is a great way to determine what the draw on the battery actually is.
The problem arises when we need to pull out fuses to try and isolate the circuit on newer networked vehicles.
ANYTIME YOU OPEN A DOOR, PULL A FUSE, OR DO ANYTHING ELSE THAT TURNS ON THE NETWORK YOUR VEHICLE IS NOW AWAKE!
What this means is that the draw will spike up and slowly drop as the network powers each module down one at a time.
This makes it impossible to pinpoint the source of the draw using the “pull out the fuses method.”
Always set up the vehicle so you can access the fuse boxes or any components you want to test WITHOUT having to open a door or trunk.
Keep the doors, trunk, and hood open and close the latches or depress the closed switch.
How Do We Locate The Draw Without Waking The Vehicle Up By Pulling Fuses?
In this situation there is an awesome tool that I want to show you.
This magic tool is called an AMP HOUND. With the amp hound you can put two probes on either side of the fuse you would normally be pulling.
The result is you can read how much amperage is flowing through that fuse WITHOUT disturbing the network!
This Is a Major Time Saver That Will Make Finding Why Your Car Battery Keeps Dying Easier
A Few Things To Remember
In this article I covered mostly battery draw, there are instances when the battery itself can become weak or shorted internally. This creates a “dead cell” condition where the battery will discharge itself.
The other thing that needs to be checked is the charging system to ensure that the battery is getting the amperage it needs while the vehicle is running.
I will jump into these in a later article.
I hope this article gave you some insights on how to find out why your car battery keeps dying, and how to fix it.
Once you determine the draw and what circuit is feeding it the culprit becomes much easier to pinpoint.
If you have a question about diagnosing battery draw comment below and I will answer your question.
Thanks for reading!