Battery Question
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Instructor
Joined: May 2017
Posts: 182
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From: Mesa, AZ
Battery Question
Like many on this site, I put my C8 on the GM battery tender when not in use. Up until yesterday I had done just small trips around town as I waited to get the car in to my detailer for PPF and ceramic. That was finished last week. So, yesterday I took it out for a drive on the highway, and it was wonderful. What an awesome machine. Altogether I put 125 miles on the car. When I got home I was surprised to find when I hooked up the BT the battery actually needed a charge. Is this normal? I guess I was expecting that driving it for 125 miles the alternator would have kept the battery fully charged. Would be interested in any constructive comments. Thanks!
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Sep 6, 2021, 10:06 AM
Race Director
Joined: Jan 2014
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From: Fulshear, TX
There are many threads on the PATHETIC CHARGING ALGORITHM GM is utilizing on the C8 to increase the MPG rating by 0.10! And I'm not sure that they are even accomplishing that.
Expect a decreased battery life. We should soon know this coming year how many 2020 C8 owners are having to replace their battery. If one is not using the charger on a 24/7 basis, expect a 2-3 year lifecycle on your C8's battery. Sustained 12.5 Vdc is only a 60-75% charged state - vs 13.2 100% charged. This 100% causes battery degradation and shortened battery life by apx 50% or more.
Expect a decreased battery life. We should soon know this coming year how many 2020 C8 owners are having to replace their battery. If one is not using the charger on a 24/7 basis, expect a 2-3 year lifecycle on your C8's battery. Sustained 12.5 Vdc is only a 60-75% charged state - vs 13.2 100% charged. This 100% causes battery degradation and shortened battery life by apx 50% or more.
Le Mans Master
Joined: Apr 2020
Posts: 6,380
Likes: 3,294
There are many threads on the PATHETIC CHARGING ALGORITHM GM is utilizing on the C8 to increase the MPG rating by 0.10! And I'm not sure that they are even accomplishing that.
Expect a decreased battery life. We should soon know this coming year how many 2020 C8 owners are having to replace their battery. If one is not using the charger on a 24/7 basis, expect a 2-3 year lifecycle on your C8's battery. Sustained 12.5 Vdc is only a 60-75% charged state - vs 13.2 100% charged. This 100% causes battery degradation and shortened battery life by apx 50% or more.
Expect a decreased battery life. We should soon know this coming year how many 2020 C8 owners are having to replace their battery. If one is not using the charger on a 24/7 basis, expect a 2-3 year lifecycle on your C8's battery. Sustained 12.5 Vdc is only a 60-75% charged state - vs 13.2 100% charged. This 100% causes battery degradation and shortened battery life by apx 50% or more.
E-Ray, 3LZ, ZER, LIFT
Joined: Sep 2007
Posts: 34,950
Likes: 12,363
From: NE South Carolina
Like many on this site, I put my C8 on the GM battery tender when not in use. Up until yesterday I had done just small trips around town as I waited to get the car in to my detailer for PPF and ceramic. That was finished last week. So, yesterday I took it out for a drive on the highway, and it was wonderful. What an awesome machine. Altogether I put 125 miles on the car. When I got home I was surprised to find when I hooked up the BT the battery actually needed a charge. Is this normal? I guess I was expecting that driving it for 125 miles the alternator would have kept the battery fully charged. Would be interested in any constructive comments. Thanks!
The C8 charging system unlike prior to the C7 is computer controlled (like the C7) to save energy. It lowers the charging voltage as the battery gets "close to a full charge." For example my 2 C7s and C8 voltmeter will read high on the 20 mile trip to town (~14 volts.) Then on the way home will lower to just over 13. That change can occur in a stepped fashion, just like the computer controlled energy saving variable oil volume (pressure reading) which is not like the "old days."
That said, I have the equitant CTEK charger sold by GM. I don't use it often as drive 4 or 5 times a week (retired so no need every day) It goes through several cycles. So it takes some time for the "fully charged" light comes on.
Last edited by JerryU; Sep 6, 2021 at 09:59 AM.
Race Director
Joined: Jan 2014
Posts: 10,709
Likes: 7,101
From: Fulshear, TX
There are many threads on the PATHETIC CHARGING ALGORITHM GM is utilizing on the C8 to increase the MPG rating by 0.10! And I'm not sure that they are even accomplishing that.
Expect a decreased battery life. We should soon know this coming year how many 2020 C8 owners are having to replace their battery. If one is not using the charger on a 24/7 basis, expect a 2-3 year lifecycle on your C8's battery. Sustained 12.5 Vdc is only a 60-75% charged state - vs 13.2 100% charged. This 100% causes battery degradation and shortened battery life by apx 50% or more.
Expect a decreased battery life. We should soon know this coming year how many 2020 C8 owners are having to replace their battery. If one is not using the charger on a 24/7 basis, expect a 2-3 year lifecycle on your C8's battery. Sustained 12.5 Vdc is only a 60-75% charged state - vs 13.2 100% charged. This 100% causes battery degradation and shortened battery life by apx 50% or more.
Le Mans Master
Joined: Apr 2020
Posts: 6,380
Likes: 3,294
No need to reply to this thread subject anymore. It gets Too many tribal replies, opinions, not based in science. Lead-acid technology hasn't changed in decades - regardless of the imersed medium. All can do as they desire. Fyi, ... nevermind.
Race Director
Joined: Aug 2019
Posts: 12,351
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From: Central Illinois
Actually the CTEK goes through a whole series of steps before it's happy. For example, mine was on my CTEK MUS 4.3 and showed green light fully charged. I unplugged it for a few minutes and opened the rear hatch, closed the hatch, and the CTEK started over again and was hours before it showed green fully charged. Surely nobody could be so foolish as to think opening the hatch one time significantly drained the battery. What you're describing is a function of the charger going through it's steps. Mine does what yours did as did my AMG MB, as did my Mustang GT, as did every car I have owned. The charging system is fine with the C8, if it was running a total loss ignition, the car wouldn't make 20 miles before it was on the side of the road.
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Brett Foote
E-Ray, 3LZ, ZER, LIFT
Joined: Sep 2007
Posts: 34,950
Likes: 12,363
From: NE South Carolina
Pic is C7 but C8 Similar
Last edited by JerryU; Sep 6, 2021 at 03:03 PM.
Moderator
Joined: Feb 2006
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From: DFW Area TX
100%. My C7 never saw a battery maintainer/charger and I replaced the battery after 5 years just because I was afraid that it might go dead on me. Never had any problems with it and I let it sit for 3-4 weeks multiple times while we were on vacation. Always started right up.
Race Director
Joined: Sep 2016
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I've had mine for 3+ months. I put it on a charger when I first brought it home, but not since. It's gotten a mix of highway miles, around town miles, and spirited country road and track miles. It's also sat for days at at a time, and a couple of times for about a week. The battery is fine, the charging algorithm is fine. The idea that it needs to be on a charger when not in use isn't supported by reality.
There were some C8s delivered with really low battery charge from sitting at BGA for so long, which led to the urban legend that the C8 can't keep the battery charged.
The CTEK always starts off in the charging portion of it's profile. Charge the battery fully, take it off the charger for an hour, then hook the charger back up. The CTEK will tell you it's charging. That doesn't mean the battery is discharged.
There were some C8s delivered with really low battery charge from sitting at BGA for so long, which led to the urban legend that the C8 can't keep the battery charged.
The CTEK always starts off in the charging portion of it's profile. Charge the battery fully, take it off the charger for an hour, then hook the charger back up. The CTEK will tell you it's charging. That doesn't mean the battery is discharged.
Last edited by Red Mist Rulz; Sep 6, 2021 at 05:28 PM.
Le Mans Master
Joined: Feb 2002
Posts: 5,394
Likes: 281
From: cumming ga
I always charge new car battery’s when I get it home. When I buy new battery’s I hook em up and fully charge it. Car charging system doesn’t bring it to full charge. I can leave it in garage for 3 or more weeks no problem.
Melting Slicks
Joined: Oct 2004
Posts: 2,187
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From: Nevada
Really? I didn't know that, so if I go out for a 30,40 minutes highway drive, how full does that charge the battery? ( I always thought that would fully charge the battery?)
After I got back yesterday from getting the new C8, I used the battery tender for 6 hours and it still didn't go fully charged (However I had the screen on for awhile going through menu and change settings, I remember it went off by itself for 3,4 times so I was on it for awhile. No problem using the screen, radio etc while the battery tender is on right? How about starting up the car while the battery tender is on? Did that by accident once before )
How long does it take to fully charge the battery with the battery tender? assume the battery is low to begin with.
After I got back yesterday from getting the new C8, I used the battery tender for 6 hours and it still didn't go fully charged (However I had the screen on for awhile going through menu and change settings, I remember it went off by itself for 3,4 times so I was on it for awhile. No problem using the screen, radio etc while the battery tender is on right? How about starting up the car while the battery tender is on? Did that by accident once before )
How long does it take to fully charge the battery with the battery tender? assume the battery is low to begin with.
E-Ray, 3LZ, ZER, LIFT
Joined: Sep 2007
Posts: 34,950
Likes: 12,363
From: NE South Carolina
^^
To save energy IF battery is 80% charged the computer lowers alternator power to what is needed for current running only and essentially stops charging. I can tell when I had voltage displayed.
Only drive 3 or 4 times a week, usually 20 miles to town. Battery reads ~14 volts going. On the way back it drops to ~13 volts!
These are the condensed details of what the C8 does to charge the battery:
The cars computer will have it enter Charge Mode whenever one of the following conditions are met;
Only if it's under 80% charge or the voltage is <12.56 will it have the charging voltage go to 14+ volts and charge with a high current. "The battery is never getting to 100%."
To save energy IF battery is 80% charged the computer lowers alternator power to what is needed for current running only and essentially stops charging. I can tell when I had voltage displayed.
Only drive 3 or 4 times a week, usually 20 miles to town. Battery reads ~14 volts going. On the way back it drops to ~13 volts!
These are the condensed details of what the C8 does to charge the battery:
The cars computer will have it enter Charge Mode whenever one of the following conditions are met;
- The estimated battery temperature is less than 0° C (32°F).
- Battery State of Charge is less than 80 percent.
- Vehicle speed is greater than 145 km/h (90 mph)
- System voltage was determined to be below 12.56 V
Only if it's under 80% charge or the voltage is <12.56 will it have the charging voltage go to 14+ volts and charge with a high current. "The battery is never getting to 100%."
Last edited by JerryU; Mar 29, 2022 at 06:27 PM.