Parasitic draw clarification

[Elizabetty]

Hi everyone. For those of you that have seen my other posts, I'm basically still utilizing all the videos and tools I can get my hands on that have been suggested but I think there's a basic concept I'm not grasping.

If I'm driving and my alternator is supposedly testing good and it's charging my battery, and my battery then drops voltage with the engine off, that would tell me there is a parasitic draw and every video I watch walks me through how to chase it. I'm getting confused as to why a draw would be initial and then stop.

For experimentation, I've used my original battery and a brand new battery and see the exact scenario between both. A fully charged good battery should still read approximately 12.6 in the morning right? Or even initially after turning the engine off? Both batteries immediately, or at least within minutes, drop down to 11.5 to 11.7 on average but they do not continue to draw throughout the night. Regardless of the amount of hours the vehicle sits, I will come back out and test and see those numbers as my average.

Isn't a parasitic draw constant? If I had a parasitic draw, wouldn't the battery continue to go lower as it sits longer? I'm not understanding something because before I can even get out of my vehicle and get set up with equipment to look at things, my battery is already quickly dropped and then it remains there in the 11 zone.

Would this be something other than parasitic draw? I may have to start all over with going through wiring and checking voltage etc to see what I missed, but I feel like I need to understand this quick drop and then hold steady concept first. It doesn't seem to match what my brain thinks of with parasitic draw since it stops after settling.

 

[Reprise]

Short answer: Yes, I think you can stop worrying, based on the info in your post.

(Apologies for the delay in updating, btw... but others have also provided info, so that's good. They've also saved me from making this a really long post, hopefully.)

First, some screencaps from my Battery Monitor app that I have on my phone, tracking the SoC on the Sierra. As a reminder, I have an isolator between the (+) terminal and the battery cable; when it's removed, it's as if the battery is not connected to the truck. However, the little device that tracks and stores this info is connected between the battery terminals 24/7. And that's how we have this info.

Pic 1 shows the battery at 12.16v SoC just before I reconnect the battery and fire up the truck.



Right after the truck is started, the alternator is charging at 14.26v. This isn't what's 'in' the battery, just what's being fed to it. The PCM / alternator detects the battery is low, so it's boosting the voltage sent to the battery. You'll see from the graph that it varies the voltage with time.



When I turn the key off, the alternator was feeding 13.88v. I removed the isolator, and the rest of the pics / graphs / info is with a disconnected battery. Notice how it takes some time for the voltage to settle down (the chemical reaction between the electrolyte (acid / water) and the lead plates.)


This is about 1hr after I started the vehicle, and 30min after I shut it off. We're at 12.42v SoC. The reaction has settled down, but you can see it's still stabilizing, and SoC continues to drop.


By 10:30pm (13 hours after starting the vehicle), SoC is at about 12.25v.


Here's the next day. You can see that now the battery voltage is stabilized, and it's holding steady. BTW, those little fluctuations you see in the line... they are variations, but we'll call them 'noise', for now. No worries.


Here, I've jumped ahead six more days... and as you can see, we're still at 12.17v. That's pretty much where we started before charging seven days earlier (30min running the engine @ idle).



About the battery... it's a 800 CCA Walmart 'EverStart Maxx' (their best FLA line when I got it.) It's almost 4yrs old, IIRC. If I leave it connected (but not driving the truck), it'll lose at least 0.1v per day (more as time goes on).

Finally, here's a chart I like to refer to. You see that at 11.9 volts, the battery will start to suffer damage if it's not charged, until it gets to the red areas, which indicate permanent damage (can still be recharged, but will never hold the same charge capacity again).


I'll continue this with a new post below...

 

[budwich]

the truck has a "I am alive mode" and "I am sleeping mode". It doesn't go to sleep right away. Depending on various circuits and states, it can take awhile. Things like opening and closing doors cause things to happen which wakes up / sets states here and there.

Where are you reading your voltages?

A "parasitic draw" is any long term draw of power. What makes it "bad" is if it occurs after the "sleep state" AND is above "normal". What's normal? Well, that depends on what's in your truck that is drawing power during the sleep state / shut off. Most trucks will likely find a level of less than .1-.2 amps. At this level, a healthy battery which might have 120-160 ahr will see about 2-5% of its power drawn out per day. NOTE: all of the power in the battery is not full "available" to be drawn out without causing an issue. Basically only about 50% should be used. From that, you can "see" that perhaps, a sitting battery might last about 10-20 days before it needs charging.... just a "thumb estimate".

As mentioned just before this post, your battery voltages seem correct in terms of charged state.. Above 12v won't be held very long after charging depending on circuit / battery... assuming your battery is connected to a circuit as opposed to just "bench charging".
The voltage will likely sit in the mid 11's normally.

Your effort needs to first have your vehicle go to sleep with key removed, then measure the draw. Then, start pulling fuses and watching the draw that is there to see where / if any drop occurs. Go from the results. NOTE: you can NOT touch any thing on your truck that causes a "prod" of the system which will wake things up. You will have to start over again if that happens.... opening / closing doors, turning key, inserting key, touching window switches, etc.

 

[Elizabetty]

Thank you. Just to clarify I was checking for draw after the car had sat for a couple hours so I know that go to sleep cycle should have kicked in and I was never finding a draw. I was convinced I had one and was doing something wrong or misunderstanding people you guys referred me to on YouTube because of the drop-in voltage after the car shut off even though I knew it was still awake for a while because it seemed like that was too many volts to drop if I'm supposed to be able to see a battery hold a full charge. When I say I'm supposed to see it, that's because I keep hearing a full charge is 12.6 and that the amount of draw after turning the engine off should be very minimal but no one was really saying it was normal then to see it sit in mid-11 range. When I hear minimal, I thought okay I'll be sitting at 12. If a normal drop to mid 11 was mentioned, I must have missed it or my ears tuned out for a second LOL

 

[budwich]

you can't measure "draw" via voltage... you need to measure current. Voltage could be "anything", current is what is going out of your battery.

one other thing... when you say your battery is "good", have you check the fluid levels in the cells? A low cell can cause the battery to have "funny issues".

 

[Mooseman]

If your battery immediately drops to 11.6 after shutting off the truck, I say your battery is bad. Have it tested at an auto parts store.

 

[mrrsm]

If you are using the tedious method of Testing the Contacts on your Fuse Panel(s) by taking the Voltage Drops on each Fuse to take the Digital Multi-Meter Readings in mV (Milli-Volts) ... These Chart Pages will allow you to convert any Voltage Drops you notice over to mA (Milli-Amps) and then Read the Results as "Current Flow" (as per @budwich ) inexorably Draining the Battery Down... like poking a small hole in the bottom of a Water Jug:

This Image shows HOW to Convert the Volts to Amps depending upon the TYPE of Fuse in use for any particular system or component and their Factory Amperage Ratings:



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Charles "The Humble Mechanic" also provides a Walk Thru on this Process: