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This topic has come up a few times, there is a lively discussion about it here, plus a full breakdown of the algorithm used by the system to maintain the battery. Hint, it is not about battery life, it is about fuel economy.


As part of it's programming, the system does maintain a full charge if the headlights are on, and headlight bulbs are cheaper than batteries, so I drive with my lights on if the trip is more than a few miles. Another wrinkle, the "Smart" system will charge the battery if it is cold out - my informal observation is if it is below about 45F or so. If it is cold, I leave the lights off.

AGM batteries sulfate much faster when they are kept in perpetual partial discharge. I learned from SFLTruck on here (who works in the industry) that cell phone towers have massive AGM backup batteries (and probably a diesel backup generator) and, much like having a smart charger plugged into a vehicle, the large and expensive to replace commercial AGM backup batteries are float charged to 13.6V plus or minus, depending on temperature. I don't drive my truck that much lately and it sits 24/7 on an Optimate smart charger. The battery is 4 years old now, and still going strong.

An AGM battery kept at a 12.2 to 12.3V 60 to 70% state of charge (where the system seems to settle if no driver intervention takes place) will have a much shorter service life than one kept fully charged (12.6+V).

One can not worry about it and replace the battery every 3-4 years, or pay a bit of attention and have a battery last 6 years or more. The simplest thing to do is drive with the lights on if it is not cold. The running lights won't do it, they have to be on. As dim as the OEM bulbs are, they look like running lights when fully on anyway 馃槅
 

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Funny, I've read this so many times about the headlamps and tow/haul mode. I can't tell that the headlamps or tow haul mode have any effect other than the lamps or trailer might drag down the battery a bit and cause a higher voltage. BUT! when turned on it sure as heck doesn't just kick up the voltage. I think this info quoted is miss read in many ways, it might even be written by one of those engineer-slash-salesmen GM is so fond of.
I can tell you it's silly to drive around playing with the headlamps and tow button to "help" charge your battery or whatever you are trying to do.
p.s. every lead acid battery's (AGM or flooded) life is shortened by it not being charged all the way, big whoop. lol our truck's charging system is pretty smart, I say just find something else to worry about.
 

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I think they (GM) turns down the alternator to improve fuel economy. Similar principal to what the hybrids do; charge the battery up when it's needed, then turn off the alternator to reduce drag on the engine when you can get away without it. This must average out to better fuel economy than keeping everything up at ~14v all the time. I'm sure they didn't factor in the environmental impact of having to replace the batteries slightly more often, but hey that part isn't included in the EPA fuel economy test so it doesn't count right?
 

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I think they (GM) turns down the alternator to improve fuel economy. Similar principal to what the hybrids do; charge the battery up when it's needed, then turn off the alternator to reduce drag on the engine when you can get away without it. This must average out to better fuel economy than keeping everything up at ~14v all the time. I'm sure they didn't factor in the environmental impact of having to replace the batteries slightly more often, but hey that part isn't included in the EPA fuel economy test so it doesn't count right?
Yes, it's all about MPG. It is kind of funny but it is kind of like a hybrid I guess. Like charge when going downhill off the gas, that kind of thing. Charge when it's really cold so it won't die, but not so much in nice weather. I seriously doubt anyone should worry too much about it though.
Nobody can guess the life of a battery and nobody seems to know how much life is reduced if it isn't a perfect 100% charge either. I suppose the AGM liking to be at a slightly higher voltage that flooded has brought this topic up more?
I think AGMs are considered 100% right at 13 volts, I don't think on my v6 truck I have seen the voltage that low very often. It seems to do a good job of keeping the battery charged. Maybe just quit watching the voltage obsesively? lol
And yes, dead batteries in the landfill has nothing to do with MPG. ahahha
We will all be rollin' on Lipos soon anyway....Don't tell a green lefty what has to be done to make those bad boys though! Oh and don't even think about what to do with them when they die. ;)
 

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I have the "diesel" AGM battery, and after letting it sit disconnected for 4 hours it is at 12.9V, I believe a "good" AGM read this way should be at least 12.8V. The chart we use for our Lifeline AGM batteries used in our Travel Trailer shows 12.8V to 13V for 100% SOC and 12.18V for 50% SOC which is the lowest you should discharge to.
 

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I have the "diesel" AGM battery, and after letting it sit disconnected for 4 hours it is at 12.9V, I believe a "good" AGM read this way should be at least 12.8V. The chart we use for our Lifeline AGM batteries used in our Travel Trailer shows 12.8V to 13V for 100% SOC and 12.18V for 50% SOC which is the lowest you should discharge to.
Using voltage to determine SOC only works if you know the health of the battery. i.e. if you know the battery is in great shape, then using the voltage will give you a reasonable approximation for the capacity (how charged up it is). However if the battery is failing (only a tiny fraction of its original capacity) it may still show regular voltage values after charging and without any load on it, but the voltage will drop very fast once you put a load on it. To test battery health (capacity) you have to put a load on it and see what the voltage is during and immediately after the load.
 

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Funny, I've read this so many times about the headlamps and tow/haul mode. I can't tell that the headlamps or tow haul mode have any effect other than the lamps or trailer might drag down the battery a bit and cause a higher voltage. BUT! when turned on it sure as heck doesn't just kick up the voltage. I think this info quoted is miss read in many ways, it might even be written by one of those engineer-slash-salesmen GM is so fond of.
I can tell you it's silly to drive around playing with the headlamps and tow button to "help" charge your battery or whatever you are trying to do.
p.s. every lead acid battery's (AGM or flooded) life is shortened by it not being charged all the way, big whoop. lol our truck's charging system is pretty smart, I say just find something else to worry about.


Next time you're running around just turn on the headlamps and watch the DIC voltage display. It doesn't change right away it takes the input and sits on it for 1 to 2 minutes. Once it starts it's trip uphill you will see that it will mosey up and hold at 13.8 or in that general vicinity. The only caveat to this is a deceleration which will run it up to 14+ and as soon as you hit the go pedal or come to a stop it will fall right back to 13.8 if the lights are still on.

I'm interested if your 16 model year works similarly to the 18 model year.
 

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Using voltage to determine SOC only works if you know the health of the battery. i.e. if you know the battery is in great shape, then using the voltage will give you a reasonable approximation for the capacity (how charged up it is). However if the battery is failing (only a tiny fraction of its original capacity) it may still show regular voltage values after charging and without any load on it, but the voltage will drop very fast once you put a load on it. To test battery health (capacity) you have to put a load on it and see what the voltage is during and immediately after the load.
Right you are of course. I have had a battery that tested at 12.6V but would not turn a starter over and voltage dropped way down under load. We deal with battery condition so often while boondocking, charging with a 230W solar, or on generator that I forget to state the obvious sometimes.

Other thing worth mentioning is that the good battery chargers will have a "de-sulfation" phase every 24 hours or so that goes to something between 14-15V for a few minutes before dropping back to 13.2V or so, and this will result in much longer battery life for anything in storage.
 

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Using voltage to determine SOC only works if you know the health of the battery. i.e. if you know the battery is in great shape, then using the voltage will give you a reasonable approximation for the capacity (how charged up it is). However if the battery is failing (only a tiny fraction of its original capacity) it may still show regular voltage values after charging and without any load on it, but the voltage will drop very fast once you put a load on it. To test battery health (capacity) you have to put a load on it and see what the voltage is during and immediately after the load.
The SOC measurement only works when nothing is hooked to it. Typically as long as the battery is at least somewhat working... The SOC measurement holds true. If not then battery is toast.

But like you said that tells nothing about the capacity or overall health.
 

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Next time you're running around just turn on the headlamps and watch the DIC voltage display. It doesn't change right away it takes the input and sits on it for 1 to 2 minutes. Once it starts it's trip uphill you will see that it will mosey up and hold at 13.8 or in that general vicinity. The only caveat to this is a deceleration which will run it up to 14+ and as soon as you hit the go pedal or come to a stop it will fall right back to 13.8 if the lights are still on.

I'm interested if your 16 model year works similarly to the 18 model year.
I've tried that and the tow/haul mode too. I haven't in any way studied it for very long but it really doesn't surprise me the lights being on will cause it to charge. It could just be because the lights are pulling power, the voltage drops, and then the system finally decides to charge. I'll mess with it some more. It doesn't surprise me it would jump up on decel because that's free charging and I think I've seen it do that.
 

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I've tried that and the tow/haul mode too. I haven't in any way studied it for very long but it really doesn't surprise me the lights being on will cause it to charge. It could just be because the lights are pulling power, the voltage drops, and then the system finally decides to charge. I'll mess with it some more. It doesn't surprise me it would jump up on decel because that's free charging and I think I've seen it do that.
It's not a pulling power thing directly.

The service manual says there are a few things (user controlled) that will force the ECM to command the regulator within the alternator to start applying field winding voltage. One is turning on the headlamps, one is turning on the wipers, one is turning the blower speed to high. Also it states that if the field winding plug is removed from the alternator the internal regulator will default to 13.8v. I have tried the first 3 above and they all take a few minutes before the ECM starts to adjust the PWM signal to the regulator to induce charging. I watched this on an oscilloscope and you can clearly see the PWM signal start to change width and duty cycle as commanded.

The part I found interesting is the timing during testing. The ECM will always invoke the PWM change but it's timing is all over the place but never over 4 minutes. This is why I was asking you to test yours, I wanted to see what it yielded just out of pure curiosity.
 

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Just a data point, but I can verify that it takes some time for the ECU to boost up the voltage. I'm in Florida and in the summer the A/C goes on full blast as soon as I start the truck. It is often several minutes into my drive before the alternator boosts the voltage. I can tell because the A/C blower suddenly gets a dramatic and obvious boost in performance when the alternator kicks in, and this often happens a couple of minutes into my drive.
 

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Just a data point, but I can verify that it takes some time for the ECU to boost up the voltage. I'm in Florida and in the summer the A/C goes on full blast as soon as I start the truck. It is often several minutes into my drive before the alternator boosts the voltage. I can tell because the A/C blower suddenly gets a dramatic and obvious boost in performance when the alternator kicks in, and this often happens a couple of minutes into my drive.

I have noticed the same thing as well.

The first time it happened, before I started investigating the charging side of things, I said to the wife hmmm seems to be a power related thing going on here. I got a manual from Helm the first thing I did was look up everything on the charging related items. That's when I realized why things are working the way they do.
 

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It's not a pulling power thing directly.

The service manual says there are a few things (user controlled) that will force the ECM to command the regulator within the alternator to start applying field winding voltage. One is turning on the headlamps, one is turning on the wipers, one is turning the blower speed to high. Also it states that if the field winding plug is removed from the alternator the internal regulator will default to 13.8v. I have tried the first 3 above and they all take a few minutes before the ECM starts to adjust the PWM signal to the regulator to induce charging. I watched this on an oscilloscope and you can clearly see the PWM signal start to change width and duty cycle as commanded.

The part I found interesting is the timing during testing. The ECM will always invoke the PWM change but it's timing is all over the place but never over 4 minutes. This is why I was asking you to test yours, I wanted to see what it yielded just out of pure curiosity.
Yes, I've tried the wipers, lights and tow haul, not high blower. I'll try it again and watch longer and see what happens. I'm assuming if one is driving at night with the lights on it should after a short time bump up to at least 13.8, correct? Even with nothing else on? Nothing but headlamps even?
What about tow/haul mode?
 

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Yes, I've tried the wipers, lights and tow haul, not high blower. I'll try it again and watch longer and see what happens. I'm assuming if one is driving at night with the lights on it should after a short time bump up to at least 13.8, correct? Even with nothing else on? Nothing but headlamps even?
What about tow/haul mode?
You know that's a great question. I would think that short answer would be yes however I've never tried that. It could be that it needs the manual input and that's what the ECM reacts upon. You've added to the charging mystery ! lol
 

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The best way to see how the voltage responds to loads is by using an amperage meter. Heavy loads versus light loads. Cold weather versus hot weather. Checking loads after recovery from a engine start versus loads during normal operation. Some manufacturers actually incorporate a process that shuts off the voltage regulator to unload the alternator until the battery voltage drops to a predetermined then kicks in again.
 

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While we are on this, my long time cheapskate back yard engineering method of load testing the battery is to either: 1) Turn the key to the on position (engine not running), put the lights on, and measure at the terminals. I figure as long as it is above 12V under that kind of load after 30 seconds, it is a good battery or 2) Have a buddy crank it while checking voltage at the terminals. The official spec is 9.6V, I like to see it over 10.

Since I have no friends and my wife thinks I am insane when I do this sort of thing, I tend to go with Plan 1. 馃槅
 
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While we are on this, my long time cheapskate back yard engineering method of load testing the battery is to either: 1) Turn the key to the on position (engine not running), put the lights on, and measure at the terminals. I figure as long as it is above 12V under that kind of load after 30 seconds, it is a good battery. or 2) Have a buddy crank it while checking voltage at the terminals. The official spec is 9.6V, I like to see it over 10.

Since I have no friends and my wife thinks I am insane when I do this sort of thing, I tend to go with Plan 1. 馃槅

BAHAHAHA Glad to see I'm not the only one experiencing that syndrome.
 

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I just had a conversation with my Optima battery Rep yesterday. He said todays new vehicles are hard on the OE batteries and that is why they came out with a new style.

They have moved to a new cell design for more performance and are getting away from the spiral cells on newer applications. The new battery is called a Pureflow and they have one recommended for the twins now.

They also made the move to only offer it in a Yellow Top Deep Cycle battery. They should fit most application in time.

I know some folks have had issues with Optima and others like me have had very good luck. I have two now in older vehicles one is 8 years old and the other is even older.

We do not see many warranties at work anymore. Most of the trouble we see are people using the wrong chargers on AGM batteries.

My luck with GM batteries on the last 4 cars has been just over the warranty till they died. It has not been good. My old Freedoms used to go no less than 10. One went 18 years. I only replaced it because I figured I was pushing it.

I expect many automakers will increase voltage soon. VW and Lincoln have already others will follow.
I tried to lookup a fitment for my 2017 Diesel and Optima鈥檚 website says none exist. What battery did they tell you works? I saw their write up about Pureflow but nothing more.

EDIT: I dug some more and found it. But it is not for the diesel, only gas. Oh well. I am still looking a good AGM.
 

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I tried to lookup a fitment for my 2017 Diesel and Optima鈥檚 website says none exist. What battery did they tell you works? I saw their write up about Pureflow but nothing more.

EDIT: I dug some more and found it. But it is not for the diesel, only gas. Oh well. I am still looking a good AGM.
I show a listing of 9048-148 for a V6 but nothing for the Diesel.
 
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