When I replaced my battery a month ago or so I started displaying system voltage when I drive and see some unusual behavior. The voltage is very high for a period of time. I haven't measured it but for the first 20-30 minutes of a drive the system voltage remains in a tight range of ~14.8 to 15.0V. Then it slowly steps down over a period of a couple minutes to what I consider a normal range of ~13.8-14.0V. This happens whether the car is fresh off the maintainer or if it has sat unconnected for 2 weeks. It also happens if I just make a quick stop in the middle of a longer drive and then get in and restart. The cycle repeats. I am guessing that it is programmed to be high to quickly recover the energy used in starting. But it seems excessive and I have never seen similar in my other vehicles. But having said that my OEM battery that I replaced was still working OK after nearly 5 years.

 

My 2017 with original battery shows voltage range 12.8v - 15.2v when I drive the car. It's been like that since new and has never caused any problems.

 

I've never seen the charging volts higher than 14.5V. My 19 GS always operates between 12.5-14.5V with my OEM battery. I noticed if you immediately turn off the running lights off after you start your vehicle the charging volts will diminish more rapidly than if you let the running light stay on. Also, other big electrical hogs I have found are the fan, air-conditioner, heating/cooling seats, Navigation and/or radio. If you turn all these features off you charging system will charge your battery more quickly.

 

Remember that when you start a car you pull over 200 amps durning the cracking sequence, not to mention all the other electrical systems that start up as well.
So, you initial voltage reading will be high to replenish what was pulled out of the battery durning this start period. It will then go down as the alternator recharges the battery.
Also most modern car charging systems don't really fully charge a battery, only ~80%. This is due to removing the load of the alternator off the engine to improve gas mileage.

 

I am an engineer, so of course I know that starting a car puts a drain on a battery and I understand lead acid battery charging behavior and voltage curves. But I have never seen a charging system behave like this one and am curious if GM did something intentional to program it to work like this.... or if mine is doing something unexpected. I am not buying that such a charging scheme is necessary since my other cars' batteries last 7 or 8 years with a stable charging profile running a system voltage of ~13.8-14.0V. I suppose an initial period of juiced up voltage might make sense for garage queens that don't get longer drives to top them up.

 

The regulator for the alternator is controlled by the cars computer. Charging can and will look wacky if you monitor it all the time. Charging is determined by a lot of parameters such as temp, battery state of charge, speed of the engine, load on the engine while running, what gear you are in and numerous other criteria.
Modern electronics, computers, make this possible.
Don't forget gas mileage too!

 

I hear you... and this makes sense that it *could* be done. But I have never seen such described in the auto press. And I have never seen it before in another vehicle, computer controlled or not. Generally batteries like stable not-too-hot charging and occasional equalizing. My other cars when the batteries are in a normally charged state run at a rock sold 13.8-14.0V. The C7 voltmeter is all over the place... but generally at what I would consider to be too high a voltage.

 

Well, let's just say GM likes doing things differently.

 

My 2019 Lexus UX200 charges the battery to ~80 - 90 % to increase gas milage. Takes a long time, 4 to 5 Hrs, to top off the battery with a Battery Tender Plus (1.25 amps).
My 2019 Honda CRV was a bit better and did not take as long (2 Hrs).
My 2017 Stingray only takes 1 - 2 hrs.
Different charging algorithms for each manufacturer.
Both my Lexus and Stingray are always kept on a battery tender when not in use.
All have original batteries.
If you really feel like there is something amiss, the only correct way for most people with out a lot of test equip is at the dealership with the proper diagnostic equip. to completely check out the complete system. Battery, alternator, computer, parasitic current draw.
Good luck

 

Time to recover charge on a maintainer is not an indication of much of anything more than battery condition and state of charge, for which there are many many variables. And no, I am not overly concerned with this voltage regulation issue. My OEM battery lasted just fine for 5 years and is now continuing to serve in the farm truck. Mostly I am curious and to see if anyone here had firm knowledge as to how GM set this system up. It is unusual, at least compared to all the vehicles I have owned or driven. Now if my new battery dies an early death from being overcharged maybe I will get concerned.

 

I never really watched the voltmeter until 12/30/2020. My original battery cranked slow after sitting 4 days and thought it's time for a new battery. FYI I think this is a great deal on a C7 battery. https://www.batteriesplus.com/produc...wer/sli48agmdp .I put that new AGM battery in it so I found the voltmeter on the DIC. On my 7 mile drive home it held a solid 14.5 volts. When I got home I put the factory battery maintainer on it for the first time. The next day I took the maintainer off, started it up and I'm seeing 12.5 volts on the voltmeter. I got my DVM out and sure enough I measured 12.5 in the power outlet by the shifter. After several hours of research here's apparently why.
1. The ECM or BCM controls the alternator output voltage by reading the battery condition and other variables. That why the extra wires are connected at the battery terminals.
2. Since the maintainer had the battery fully charged, it lowers the alternator output.The maintainer puts out up to14.4 volts and 3.3 amps.
3. I took it for a 20 mile drive. About 10 miles into the drive I turned on the headlights and rear defogger to help pull down the voltage. The voltage slowly increased to 13.5 volts. I'm going to not use the maintainer until the alternator gets back to 13.8-14.2 volts and put the maintainer back on to see if I can repeat the low voltage issue. I'm 99% confident I can!
4. New batteries are supposedly only about 50% of full charge, that's why it was charging at 14.5 volts on the way home after the new battery was put in and only 12.5 volts after the maintainer was on for 24 hours.
I was afraid I needed a new alternator, but after much research, it looks like it's working like it was designed!

 

Your alternator/battery/maintainer are really working perfectly. Your new battery is one of the best AGM batteries you can purchase for a Corvette. Should give you many years of useful service. Because this battery has such a large charge capacity it will not drain as quickly as did the OEM battery. If you want to put a high drain on the battery try putting on the high beams, the heated seats, the air-conditioner, the fan on maximum, and the Navigation system. 12.5 volts is what I normally see on my voltmeter as I keep my OEM battery plugged into the maintainer every time I am not driving the vehicle.

 

And that my friend is why I haven't purchased a GM vehicle since I purchased my new 1967 Chevelle and when I bought my brothers used 1975 Vette ( what a piece of crap that was ) in 1980.
Rich

 

You might not have to wait too long. GM, Ford, Chyrsler all have serious debt problems. GM is the worst. They are billions of dollars in debt. If the Federal government doesn't bail them out in the next year or 2 they may go bankrupt. Financial experts speculate that these 3 car manufacturers may all merge together if they are going to survive. Big trouble ahead.

 

If they didn't pay their CEO's tens ( maybe hundreds ) of millions of $'s for just sitting in their offices and twiddling their thumbs and correctly building a car the first time they would not be in this condition .
Rich

 

I think it's a little more complex than that. Chances are we will never see a C9. GM is in huge trouble.

 

What am I missing here?

 

MMD: "I think it's a little more complex than that. Chances are we will never see a C9. GM is in huge trouble." video follows.

I love how the internet has made soooooo many people financial and economic geniuses. Truly amazing! ! ! !
AND the message is usually the sky is falling - the stock market is crashing and gloom and doom is right around the corner...oh my! 😨

How we got from a discussion about voltage regulators to Ford, GM bankruptcies always amazes me....

 

The OP's experience with voltage levels pretty much mirrors mine. I've got a 2016. The battery was replaced in 2017 by the previous owner. No electrical/charging issues that I'm aware of.

 

What do you want to know. I've had Chevy's since I was a kid, not a ton like some of us have had but they are, '55 2 dr. Bel Air - '65 Impala - '67 Chevelle 327, my brothers '75 Vette after he purchased a 1965 Yellow Coupe and now my '19 GS. The only reason I purchased a 'Vette is because it is just that, a beautiful car.
Rich