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Discussion Starter #1
Have 2017 Colo with 11K miles and just returned from 5,000 mile trip where I spent a lot of time (too much according to herself) watching the battery charge status. Super impressed with truck but have issues with the charging algorithm and wondering what others are experiencing.
Mine sometimes resists going into charge mode but finally does and charges around 14.3-15.0 Volts which is very reasonable for the absorption phase. The problem is that when it leaves that charge phase, it drops the voltage to 12.1-12.2 and holds it there, often for many hours before charging up again and the recharge phase is often very brief, several minutes. A 12.1-12.2V battery is only 50-60% charged. My battery voltage in the morning before I start the truck is usually 11.8-12.1 volts, not the 12.8-13.0 it should be for a fully charged battery. Sulfonation can start occurring when a battery is discharged to less than 90% if it is not quickly taken back through an absorb cycle and that can permanently damage a battery pretty quickly.
I have been off grid at home for years now and "float" voltages, i.e. where the system maintains the battery bank to prevent damage and is considered a full charge is typically 13.5 volts. I can't understand why the truck battery should be much different since the chemistry is the same in home and auto systems.
I'd be sort of OK if the charging system held the battery at 12.7-13.0 volts which is nominally considered to be a full charge but why does the system hold the charge at 12.1 volts? Are others noticing this or is my system having issues? The alternator is absolutely fine because when the charging kicks in, it has no problem delivering enough current to get the battery to good voltage quickly.
Here's a general chart of battery charge versus % charge (SOC - State of Charge).
 

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Discussion Starter #3
I watched the DIC while driving but confirmed its accuracy with volt meter on battery terminals. Morning voltage test before starting was with volt meter as well.
 

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rockcrawlerdude - since the DIC is confirmed accurate, should it matter if I use that to monitor battery voltage? one thing i am confused about is that when the alternator would kick in, the voltage would rise from 12.1 to 14.5 or so in less than a minute. a battery truly at 12.1 should not be able to achieve high voltages for a long time, not til after going through bulk and part of absorption cycles. so, i am not totally sure what the DIC is telling me. it would be really nice to have an ammeter as well to watch.
 

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I just asked because when installing the sensor wire for an alternator in a build, there are big differences depending on where you pickup your voltage.

Voltage at the dash can be a full volt lower than voltage at the battery. You get voltage drop along the system. So, if you want more charging from your alt, you run your signal wire further from the alt/Batt so it ramps up its charge. If you pick up voltage signal from the bat or directly from the alt (such as in a 1-wire setup) then it reads higher volts and is satisfied.

I Figured the DIC would read lower than the actual battery posts

I don't understand what you mean when you say "when the alternator kicks in" but I'm not very familiar with modern electrical systems in cars. More familiar with old simple cars.

Trying to help just by kicking around ideas.

My meter is in my work truck, otherwise I would check mine and compare
 

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Discussion Starter #6
I see what you mean but I assume that chevy would want the DIC to reflect accurately the voltage at the battery, otherwise I am not sure how you could use the information. They could limit voltage drop in a number of ways or have a correction for it. As I recall, the DIC V was within about 0.2 V of my meter and that's about as close as meters can be expected to be anyway. All I mean by "kick in" is that something triggers the charging system to ramp up the voltage, i.e. start a charge cycle and that's when the alternator churns out amperage at whatever voltage it's supposed to.
one thing I noticed that is very cool about the charging is that the system is smart enough to start charging when the truck senses it is trying to slow down. In other words, when I'd brake to slow down from hiway speeds, the alternator would kick in, which puts a drag on the engine. I'd notice this virtually every time I'd slow down or coast off high speeds. Basically, the truck is using the charging system to help slow down the truck while getting a "free" charge out of it. I suspect this feature is built in to help increase mileage as I noticed the system almost never charges while the engine was under a big load (like hauling up climbs) but would often kick in when decelerating or coasting. I'd like to get confirmation of this from other users if possible. It's a subtle way of eeking out a bit more mileage over the long term.
My WAG at this point is that something in the logic circuit isn't quite right and the charging system is erring on the side of fuel efficiency and not kicking in often or long enough to adequately charge the battery. I also believe that the float set point is too low and should be 12.8-13.0 V rather than 12.1 or 12.2.
Very curious any observations others have made.
 

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Just to follow up, I am seeing the same numbers as you on my DIC. I have not done any verification with a multi meter.

Only paid attention for about ten mins because I have a short attention span.

12.1-12.2 seems to be normal while driving or stopped
13.0-14.8 coasting or decel w/ brakes
14.5 about 30% of the time while driving

idling in park it'll go through phases and be 12.1 and then it'll hop up to 13.5-13.8

Just did this to try and help you with your data.
 

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Discussion Starter #8
Thank you very much for looking into that. Mine doesn't spend anywhere near 30% time at elevated voltage but that may be because i was at hiway speeds a lot of the time. Either way, I can't imagine why they have it set with a base voltage of 12.1 and will be contacting GM corporate to get their response. I will post what I find.
 

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Discussion Starter #9
Dealer told me today that my charging system is fine and that 12.1 volts is normal, controlled by ECM, and not adjustable.

The information sheet for the ACDelco AGM49 battery my truck came with says 12.7 volts is considered a full battery, consistent with everything I have learned about lead acid 12V batteries. 12.1 volts is a seriously discharged battery and is certainly undergoing sulfonation, poisoning the plates.

Here's a link to battery maintenance facts:
http://www.batteryequaliser.com/products/product_battery_maintenance.htm

It is very difficult to see how a voltage of 12.1 can be justified while the car is running in light of overwhelming evidence that that will greatly shorten a battery's lifetime.

In fact, while towing I noticed that the truck was actually pulling down my trailer battery and started disconnecting that while on the road. I solar recharge that battery and even with minimal recharging it sits at 12.7-12.9 volts in the morning after a night of usage whereas my chevy battery sits at 12ish. That is bad, bad, bad for a battery and will absolutely kill it over a not very long time.

My growing concern is that Chevy is intentionally sacrificing battery life in order to gain fuel efficiency, which of course they are trying to maximize across their fleet to meet federal standards.

I have opened a discussion with GM corporate and will let people know the outcome.
 

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I've been watching mine since seeing this post. I haven't seen it go below 13.7 mostly sits at 13.8 - 14.4 I drive stop and go for 23 miles so no real highway driving.
 

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Watched mine for about 15 miles tonight. At 70 mph it was 13.8 at 60 and under it was 14.5 ish. Parked on the driveway for few minutes when I got home, still at 14.5 ish.
 

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Discussion Starter #13
Hey, Thanks for all the feedback and data! I hadn't checked in for a few days and don't get email notices for some reason. I wish mine were working like you guys is. Dealer says mine is performing correctly and GM corporate says that as long as the dealer says it's ok then there's nothing else to be done.

I hooked mine up to a nice taper-charge battery charger for a few days and that brought the resting voltage up to around 12.8, where it belongs. Any time I drive though, the V goes down to 12.1 V and the ECM keeps it there. Basically, the truck is using the battery to run. When I come in and park and turn off ignition, the Voltage gradually climbs back up.

Any suggestions how I can appeal this with the dealer? Is there any recourse when the dealer says it's working right even though common sense, observations, and all the battery information in the world says it isn't?
 

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may sound crazy, but I'd almost take it to auto zone and have them do the alternator load test on it. If it passes great, if not there's nothing like showing up at the dealer and telling them auto zone's tester says they are idiots.
 

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Discussion Starter #18
Rockcrawlerdude (RCD), it continues to amaze me the resources you lay your hands on. But, I admit, I don't know how to interpret the chart you posted here. Does this imply that if the battery is considered fully charged, the "generator" (it's an alternator isn't it??) will only turn out 12.1V? What should the resting voltage be or is it not possible to tell that from this chart? If the alternator is only turning out 12.1V, how can the battery be maintained at a healthy voltage, more like 14V?
EKarlW and I seem to be seeing the same thing whereas Rockcrawlerdude, burgess, and andyz71 seem to show theirs never drop into the 12s although I thought RCD did say earlier that his also stayed low for periods of time "12.1-12.2 seems to be normal while driving or stopped".
Part of me wants to believe that the charging algorithm is complicated and that Chevy has it dialed in both to maximize fuel efficiency and battery life. But the part of me that maintains the battery bank in our off-grid solar system struggles to understand why the charging system would ever let the battery voltage fall below 13V unless the alternator were mechanically incapable of keeping up with demand, which is not the case.
RCD, the chart answered the question for you but you can you please spell it out more for me because I am clearly still missing the point and not understanding why extended duration at 12.1V is OK?
 

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I interpret this chart to mean output Voltage is based on electrical load. I thought it would put your mind at ease to see those low voltages in the normal operating range

Probably why I see 14+ volts anytime I’m towing (because I run with my trailer lights burning) more load, more volts.

Did you notice if the battery is AGM (absorbed glass mat)? I believe they are. Those are batteries that can handle quite a bit of abuse and discharging unlike old school car batteries.

I bet GM has this figured out (they do make electric cars, too) ;)
 

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Also, IF GM is “cheating” the battery to get more mpgs out of the truck then it is already a caclulated risk for them. Meaning they’ve decided it is worth it and they likey won’t admit that to you.
 
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