SOLVED! Battery needle hangs then jumps but everything fine?

[Elizabetty]

Ugh.
I understand dash gauges are excellent approximates, not perfect, but I'm frustrated that I am continually told my charging system is fine. I feel like this isn't the gauge being weird because it only happens when the vehicle has been sitting for a long time.

In the morning, I turn the key over and see my battery line just above the split between 9 and 14. I start the engine. Needle drops to zero, moves back to where it was with key on and then hangs for a bit. Alternator is doing its thing and the engine doesn't seem to be having any problem. Then suddenly the needle for the battery will jump to 14 and exceed a bit beyond it and then settle down and do its normal home. This has been happening more and more frequently as the winter goes on and the hang time seems to be getting milliseconds longer with each morning.

Yesterday at an auto parts store, I was told the battery was 12.4 and good with the engine off before they ran the tests. (That's a question for me right there because 12.4 to me seems good but not good enough.) Then I drove to a different auto parts store 30 minutes away knowing that my battery should be fully charged by then driving at highway speeds. I got there and they said the battery was 13.6 or 13.8 I believe with engine off. Then they tested everything and said everything is good.

The test at the first auto parts store was done after sitting in the parking lot for approximately 45 minutes to an hour with engine off. I feel like that is the most accurate reading and the reading immediately after arriving at the second auto parts store was likely affected by something called float charge?

My battery has a sticker of 6/20 on it with an install date of 9/20. Interstate brand. CCA 800.

I lean toward this being a battery problem because auto stores, not repair shops, don't even try to sell me a battery because they say mine is fine. Alternator does not seem to exhibit any problems either. I don't hear a typical bad alternator noise, nor does it seem to get hot. Belt seems ok. Also seems to be doing its job when it gets that battery up to par in the morning. I watch and listen and there is no change in function that suddenly makes the battery start charging. It starts up, does it's thing, but it's the battery that seems to lag behind.

I feel like the battery is low, or weak, and once the alternator gets it up to where it needs to be, that is why the needle bounces up. I don't think the gauge is broken and I don't think it's my alternator. Why am I being told my battery is fine?

Additionally, for anyone reading this that is aware of my other electrical problems, I understand what parasitic draw is as far as cause of battery drain. I am specifically looking to understand the lag and if that means I have a weak battery or not, regardless of what's causing it. Pretend there is a perfect world with no parasitic drain and help me diagnose this symptom.

Thanks everyone! Have a fabulous monday!

 

[Blckshdw]

You could try buying a bluetooth battery monitor, so you can see what it's condition is on your phone, without having to pop the hood. I have the semi permanent one, but they also have one that clamps onto the terminals for a few $$ more.

Amazon.com

https://www.amazon.com/dp/B087R3FWQM/?tag=gmtnation-20

At least this way you could see what the battery voltage is, in case there's something between it, and the signal getting to the cluster. Maybe help confirm if the battery is indeed good, and the problem lies elsewhere.

 

[christo829]

Our vehicles also have a feature where the charging system does not immediately go to full load on the alternator when things are very cold. Mine usually doesn't do it until temps get down in the teens, and the truck's been sitting. It did it a few times during the Christmas cold snap, but temps are a bit milder here in VA than they are in WI.

If it does it when it's still warm, *that* might be indicative of a problem, but if it's only doing it after sitting and getting cold, it's not a problem, it's a quirk. We only have a few on this platform, right?

Cheers-

Chris

 

[Reprise]

Ugh.
I understand dash gauges are excellent approximates, not perfect, but I'm frustrated that I am continually told my charging system is fine. I feel like this isn't the gauge being weird because it only happens when the vehicle has been sitting for a long time.

I'm gonna give the abbreviated version for now; there's a lot to be discussed / read. But from your descriptions...

You're OK. Don't worry. And Interstate produces a decent-to-good quality battery, relative to other brands.


Continuing on..

In the 'old days', what controlled how much current was being fed to the battery by your charging system (alternator), was a 'voltage regulator'. These days, they're contained within the alternator internals; in the 'really old days', they lived outside the alternator.

Our (and many other GM vehicles) have another device that helps out with the controlling of the current. Of course, I forget the acronym / name of the thing, but it's 'smart' enough to take a few factors into account (ambient temp, State Of Charge (SoC), voltage demands, engine speed, etc.) and control the flow of current a little more precisely. At this point, most new vehicles likely have a similar system. Someone else will remember the name / acronym and add it to the thread, I'm sure.

Some numbers, for Flooded Lead Acid (FLA, or 'conventional') 12v batteries... you can read SoC with your multimeter, set to DC volts... (to two decimal places, if you have that option)

'Full' charge: 13.6v. Note that you'll only likely see this if you have the battery on a charger, and it goes into 'float' mode. Don't expect to see a battery here long, unless it's on float.

"50% SoC" or better" -- Where you want to be with a FLA battery. This is about 12.06v. Anything between 12.06 and 13.6, then, is just fine.

"11.9" -- This is 40% SoC, and if you have a battery that is at this voltage or lower... it needs to be charged a bit. Between 11.9 and 11.58v, the battery is still OK, but definitely charge it (whether that be from running the engine / alternator, or putting an outboard charger on it).

"11.31 and lower" -- This is where permanent damage occurs to the battery, in that some capacity will be irretrievably lost. You'll still be able to charge / start a vehicle, but the battery will never operate at 'full capacity' or 'full amperage-hours' again (until it's recycled, and that's another story).

"10.5v and lower" -- This is 0% SoC. Depending on how long it's been like this, you may be able to recover the battery (temporarily) with an 'intelligent' charger, but if it's been awhile (like weeks or longer)... "she's dead, Jim".

"30-45min" -- This is how long you need to wait after a charge for the battery to 'settle down' and give a proper reading. Doesn't apply to 'float charging' as much, b/c the current to maintain 13.6v is so low, but it's still the most accurate way to measure SoC.

"3 years" -- Marginal batteries last about this long, from new, before they start giving trouble. A FLA battery *can* last 5 (or more!) years, but the harsher the conditions, the shorter it lives. Summer heat is the enemy of a battery, but you may not see it 'fail' until the cold of winter (it can't store the full 800 CCA any longer, when your vehicle needs it).


And now, a couple of numbers related to charging:

14.xx to 15.xx volts -- Charging a battery isn't 100% efficient, so a battery charger will put this amount of voltage into a battery to raise the SoC. And it will raise / lower the voltage between these parameters to do it (so if you're in your vehicle, you may see it move a bit -- but not fluctuate wildly). Your alternator can charge at this rate, if needed, although if you see your dash gauge above 15v for any significant period of time, you may have an issue with your system. Don't be worried if your gauge goes >= 14v; the system is putting charge in, optimally. If the vehicle has been sitting awhile, you'll likely see the needle in this area for a bit.

Finally... When you have some time, head over to www.batteryuniversity.com and check out the sections on FLA batteries for a good primer. There's a lot to go over there, especially if you start getting into the other battery chemistries, like AGM, etc., or the 6v world (RV people!), etc. So have a cuppa of your beverage of choice at hand, while you're reading.

 

[Chickenhawk]

Sounds a lot like a stepper motor problem with the gauge.

 

[Mooseman]

I concur with @christo829 , it's the alternator control. The PCM will delay turning on the alternator as a belt saving measure when it's really cold. The colder it is, the longer it will take after starting the engine.

Our (and many other GM vehicles) have another device that helps out with the controlling of the current. Of course, I forget the acronym / name of the thing, but it's 'smart' enough to take a few factors into account (ambient temp, State Of Charge (SoC), voltage demands, engine speed, etc.) and control the flow of current a little more precisely. At this point, most new vehicles likely have a similar system. Someone else will remember the name / acronym and add it to the thread, I'm sure.

That would be the SARVC however it wasn't implemented until 2006 (hers is an 02). I see my 07 drop below 14v after driving a while and the battery is charged. When I turn on a heavy load, it comes back up. I only notice because the wipers will be slower. It helps to extend the battery life.

I think your battery and alternator are fine.

 

[Reprise]

Forgot to mention earlier... I have the device @Blckshdw mentioned as well (the semi-permanent kind, like him). Been using it on my Sierra, which *does* have a parasitic drain issue that I've been too lazy to dig into. On that truck, I have a battery disconnect installed, because the truck sits a lot. But I can leave the monitor connected across terminals, and see the SoC at a moment's notice w/ the phone (Bluetooth, so you have to be near it).

About a year ago, I was notified of a firmware update (for the box itself), and the app stopped working afterward. But when I got a new phone a few weeks ago and opened the app on it -- it works again (better than it used to, because the BT connectivity improved -- I can connect to it from much farther away, now).

Amazon carries a couple of different versions, but they all work the same -- small device that connects to the battery, and an app that you download to connect / pair to it.

Might be overkill for a vehicle that gets driven on the regular, but it's perfect for one that isn't, IMO.

 

[budwich]

you can buy $5 lighter plug devices that provide a voltage output reading "continuously".... plug it in just before you try your start to see what the voltage is and watch it there after. Don't leave it plugged in all the time as it will draw down your battery if you don't use your vehicle regularly.

 

[Elizabetty]

Thanks everyone! I'm going to stop worrying about my battery. Thanks for the super thorough explanation and suggestions! Consider this one a done deal for me and close 'er out. Lol