Car has a dead battery again? Learn how to find out why

“My battery keeps dying, I bought one at Walmart and put it in yesterday, but it was dead again today.” What can it be?

I could bet many of you have heard this once or twice before, it’s understandable for the customer to think. “well the battery is shot, throw one in please.”

I mean right? The thing is dead, it must be bad. What happens when you install a new one and send your customer on their way, just to get a call the next morning from a now angry customer telling you their car won’t start again?

Checking for battery draw is a pretty straight forward process that should be done when a battery continues to lose its charge over a short period of time.

First off let’s load test the battery and charging system. These items need to be confirmed ok first. If you have a tester such as the Snap-on D tac this is a pretty simple test.

All of our tests came back ok. The battery is good and our alternator is charging properly. Let’s check the draw. We basically need to put our meter inline between the battery negative terminal and the negative cable on our vehicle.

Keep in mind here that I am just going over sheer basics here, I can, and will go much deeper into electrical draw diagnostics in another post.

We are now reading a high Milliamp draw from the battery, 1448 is considered pretty high.

Anywhere from 20 to 80 Milliamps is acceptable battery draw 80 being a little on the top side of acceptable.

In a vehicle that is driven every day it’s borderline.

A few things here to note, we are inline on the ground side. My meter lead is plugged into the AMP scale, there is a important reason for this. The meter itself has fuses. These are to protect against overload.

On the amp scale you are fused up to ten amps. The Milliamp scale is only fused to 400 Milliamps.

So lets say your meter is hooked up and there is a big spike in amp draw, possibly a door opened, or the draw is very high for whatever reason. If you are plugged into the milliamp side of your meter guess what?

You have just smoked your meter fuse, if your meter is a cheaper model, you have smoked your meter.

By hooking our lead into the amp port, we are protected to 10 AMPS. We can then use the range button to step down to Milliamps for our reading.

Still there? Good, before we go any further let’s talk about a few things. Depending on the vehicle, you will be dealing with a can network.

Can networks are another topic in itself that I will go into depth on in a different article.

For now we just need to think like a technician, we need to prepare and plan, anytime you connect or disconnect that battery you are going to “wake up” the network. If you open a door, or disturb the vehicle while working this network line wakes back up and your initial startup draw will be very high.

Depending on the vehicle you will have to wait up to twenty minutes for the line to shut back down.

This can make finding a circuit draw very difficult. If every time we open a door to get to a fuse box, or pull a fuse from a circuit it’s gonna wake up. Then we have to wait to see if the draw is lower when things shut back down, this is downtime that we need to avoid.

The first way to set up properly is to open all the vehicle’s doors and trunk, then simply roll all of the latches closed. Do the same for the hood.

In a nutshell make sure you can get to any fuse boxes or components for testing without having to “wake up” the can network of the vehicle.

Once we have the meter hooked in we want to see the live draw reading, all of this after the vehicle has been sitting for a short period of time. Now is when you want to press the min max button on the Fluke 88, this will start recording the draw to give you the information you need.

It is entirely possible that the can network is not going to sleep due to a faulty component, this can be determined by letting the vehicle sit for about a half hour give or take depending on the vehicle. If we come back and our draw is very high this could very well be the case, but we have to rule out possible other causes first.

In this example we will use the readings from our Volvo.

After sitting long enough this vehicle’s battery draw has dropped from 1448 to 158 MA, this is a good indication that the network has gone “to sleep.”

This is good but we have to remember we are looking for 20 ma, up to maybe, if we are pushing it 60 to 80 Milliamps.

If this vehicle sits for a few days the battery will most likely be dead when our customer attempts to drive the vehicle, this of course is depending on the condition of the battery. This is why it is so important to check for these draws.

if we just put a battery in because the old one tested weak, the new battery will most likely take a little longer to discharge, but it will. Make no mistake, you have only fixed half of the issue and you may end up with an angry customer. or stuck if you are a DIY.

Listen, if you care about your customer, your business, and your reputation, you need to cover these details. The shop that load tests the battery, slams one in and sends the customer on their way is not providing the best value to their customer.

The shop that replaces the weak battery, and finds the draw that would have caused the customer to hear nothing but “click click” in the garage when their kids are in the back, ready to go to school.

Or the person that would have been late for an important meeting because their battery was dead again. You will be an asset to them.

This day in age there are multiple ways to market yourself, online, mailers, whatever, but remember this truth. Word of mouth trumps them all. If people are talking in their circle and they have a story like the one above to tell, it will reach people on an emotional level. It will never be forgotten. Trust Scoot on this, strive to build up a good reputation with your customers. If you are a DIY person it’s just as important.

You don’t want people in their household to say “the car needs service, what shop should we call?” You want , ” the cars not starting, call Scoot.” You get the idea.

Again, if you are a DIY you still need to do it right.

Moving on…

We have let our car go to sleep long enough, we can clearly see the main consumers are shut down, if you were to watch the meter the whole time you would actually see the network drop down in stages during this period. Now we see that at 158 Milliamps we are still drawing a little too much power out of our battery.

Now is when we do a quick visual inspection, remember how we opened up the doors, hood, and trunk and then rolled all of the latches closed? We can now go into the vehicle and look around without waking any thing up.

Think of it like tip toeing out of your cute little baby terrors room, desperately trying to avoid waking the little one by stepping on any toys or Legos on the floor. Scoots off course. Make sure obvious things are not on, overhead lights, car chargers, glovebox light,etc

The point here is you are not the rookie that waited a half hour for the network to go down just to pull on a door handle so you can start looking for the issue, just to have the good ole network wake up and scream START OVER DUMMY! Scoot’s been there more than once, damn smart ass cars.

So we look around and see nothing obvious, what’s next, what’s eating that power? There are a few ways to deal with this. The first old school way is to remove fuses one at a time and see when the draw drops down on your meter.

Then you would find the wiring schematic and trace everything on that particular circuit until you find the greedy component. It’s good and it works, the problem is with newer cars every fuse you pull will wake the network up again. You will then have to wait for it all to go down again before you see if you even got the right fuse. If you have forever this is good, but not very practical.

Next we can use the amp hound, with this tool we are able to test each individual circuit via fuses, without removing any fuses. This allows us to pinpoint the fused circuit that is feeding our parasite. Here is how it looks.

The tool will tell us when it has made contact with the fuse, if it beeps steady we move on. When it gives you multiple beeps it’s telling you that the fuse you are in contact with is feeding something.

This starts to narrow things down a bit. You can see exactly how much power that fuse is feeding out.

The tool is reading a draw at the 10 amp fuse I am in contact with in our example.

Keep in mind the amp hound is not a Fluke 88 so really I only look for the amp hound to sense amperage draw, I always take the reading on the Fluke as the actual draw.

Think of the amp hound as the whistle blower here, not a meter.

Running down every fuse you will find some that have slight draw and some that have more draw, this is where I print out a schematic for the vehicle’s power distribution and start making notes on all of the fuses.

Ill write “ok” next to no draw fuses and write “check” on the ones that give a reading. Remember we cant just start yanking out the fuses that have a slight draw yet, we have to lay down the strategy first.

One thing I do want to point out is there are many much more complex issues with electrical diagnoses. I’m trying to keep this very basic. I will do a post on more advanced diagnoses for electrical later on. This includes lab scopes and more complex setups.

One quick, more advanced trick is you can do is, wrap an amp meter clamp around a wiring harness coming out of a complete fuse box.

This will narrow down what fuse box is supplying our draw. This helps in targeting vehicles with multiple boxes, then you know you are in the right spot to start looking.

It’s really all about breaking it down into smaller pieces until there is only one left with this electrical draw stuff.

Moving on, I have checked all of the other fuses. This ten amp fuse is the highest draw on our amp hound, it’s location is number 15 in our engine compartment fuse box. Let’s see what it powers…..

Ok, so now let’s pull out that fuse, make sure you mark the location so we don’t mix anything up if we end up having to remove more than one fuse.

Awesome! The draw has dropped down to acceptable limits, all that is left to do is look at our wiring and trace out all points that are fed by that fuse.

In this case the glovebox door was warped, causing the door to shut but not fully contact the switch, leaving the glove box light on.

That is how you find electrical parasites.

Honestly this was a very simple one to just get the basics out there for you guys. I will definitely get into some real world complex issues on another post.

Please comment below with any questions or ideas, if you liked this hit like and I will post more on the subject.

Thank you for reading, happy hunting…..Scoot