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I use the Battery Minder on my C4 & C5 & have for years. I have a cigarette lighter attachment & plug them in the center console & feed the wire out the window I leave slightly open. The only on 'power always on' accessory plug in new C7 convertible I got 8-20 is in the trunk. I now have 133 miles on it. I have the dashboard display in Touring because I like the extra info always displayed. When I get in & just press start to put auxiliary power on, I can see the voltage readout which is 2.9. When I start the car, the volts go into the high 13's & low 14's.

My issue it the resting/cold volts. I believe I should be seeing a minimum of 11.8 volts.

I am not closing the trunk on the cord since I'm sure overtime there will be a depression in the trunk weather strip. I bring the trunk to it's lowest, non-closing position. The trunk light times out after 10 minutes so I didn't see that as a problem. The Battery Minder does go into float mode but compared to my other cars it takes much longer. If I unplug it & plug it back in 5 minutes later, it may take 45 minutes to start blinking again.

Am I doing something wrong with this hook-up or did I get a bad battery off the production line.

Any thoughts are appreciated.
 

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Welcome to our forum POLOG91. The use of the Corvette maintainer or a CTEK 3300 (same as the Corvette and they make the one for GM) has been covered extensively here, as well as the fact that you can safely close the trunk on the maintainer cord (please use our excellent search function if you would like to see the posts). As to reading only 2.9 volts, that clearly is not you battery voltage since the engine would not budge at that level. I am not sure what you see when you press the accessory setting, perhaps others can chime in.
 

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Thanks for the replies. I had already seen the previous threads. I didn't see that any of them addressed the cold battery volts. I've got the car in Sports mode but I have set the dash display to the Touring mode theme. In that theme, on the right side of the display, the are always certain readings displayed, like voltage. That is where I see the 2.9 volts before I start the car.
 

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The 2.9 volts may be some auxiliary voltage reading before the system fully energizes. Since the voltmeter is not old style running directly to battery, it most likely runs through the body module and/or several others before it reaches the gauge itself. As jsvette mentioned above, if it was truly the system voltage the car would be dead in the water and nothing would operate.
 

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Thanks for the replies. I had already seen the previous threads. I didn't see that any of them addressed the cold battery volts. I've got the car in Sports mode but I have set the dash display to the Touring mode theme. In that theme, on the right side of the display, the are always certain readings displayed, like voltage. That is where I see the 2.9 volts before I start the car.
I have no idea what that display is reading when the car is in aux mode or on without the engine running but it's not accurate, don't fixate on it. The gauge displays come from the computer, they are no longer directly connected to anything so unless the engine is running they are of no value.
 

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Thanks for all the input. I didn't know the volts info wasn't direct from the battery. I was fixating on this ... 3 weeks prior a battery on a Battery Minder stranded me. It was so dead it couldn't be jumped. The battery was 8 years old, not bad. Anyway, my car has been operating just fine. Taking the info from greggshere & mjw930, The 2.9 volts is probably some representation of the float charge from the Battery Minder being read by the computer.
 

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The 2.9 volts may be some auxiliary voltage reading before the system fully energizes. Since the voltmeter is not old style running directly to battery, it most likely runs through the body module and/or several others before it reaches the gauge itself. As jsvette mentioned above, if it was truly the system voltage the car would be dead in the water and nothing would operate.
You’re seeing 2.9 volts because that receptacle shuts off when the engine shuts off, or shortly thereafter! That is not a real voltage just feedback from one side of the line-it has not real power! You must use the always connected receptacle in the trunk. Many folks have said they close the cover with no ill effect on the seal. If that bothers you get an extension if that can be routed in a vert.
I was concerned about low voltage at 12.4 volts. It should be a minimum of ~12.8 on a new battery. That is read ~24 hours after running the car to get past the surface charge the ~14 volts alternator provides. My C7 has run fine for 11 months so I stoped being concerned!
 

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You’re seeing 2.9 volts because that receptacle shuts off when the engine shuts off, or shortly thereafter! That is not a real voltage just feedback from one side of the line-it has not real power! You must use the always connected receptacle in the trunk. Many folks have said they close the cover with no ill effect on the seal. If that bothers you get an extension if that can be routed in a vert.
I was concerned about low voltage at 12.4 volts. It should be a minimum of ~12.8 on a new battery. That is read ~24 hours after running the car to get past the surface charge the ~14 volts alternator provides. My C7 has run fine for 11 months so I stoped being concerned!
The 2.9 volts reading has nothing to do with any receptacle shutting off. He's getting that reading from the digital dash display before the car starts. His comment on the front receptacle was on his C5/C6, not the C7.
 

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The 2.9 volts reading has nothing to do with any receptacle shutting off. He's getting that reading from the digital dash display before the car starts. His comment on the front receptacle was on his C5/C6, not the C7.
Yep, I misread where the 2.9 volts was being read. Still probably the same issue, it is not measuring the battery voltage but for some reason one side of the 12 volt power with the other not connected or going through a high resistance path when on auxillary. I do not know why. The way I use to measure the battery voltage with the car shut off and so there are no interior lights on etc. is with the hood open and checking at the alternator terminal and ground after waiting for all lights to shut down.
 

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UPDATE - I've had my car almost a month now with no battery issues. It is annoying to me that the cold volts reading isn't 'true' but as soon as I crank up the engine the numbers jump to the 14's. Thanks again to all who helped explained this.
 

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UPDATE - I've had my car almost a month now with no battery issues. It is annoying to me that the cold volts reading isn't 'true' but as soon as I crank up the engine the numbers jump to the 14's. Thanks again to all who helped explained this.
Just keep in mind when the car is running, you are reading the charging system, not the battery. The battery must be read with engine off.
 

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Just keep in mind when the car is running, you are reading the charging system, not the battery. The battery must be read with engine off.
Agree, in addition after the car has been running there is a higher voltage surface charge on the battery, which depletes over time. I measure battery voltage after the car has been sitting 12 plus hours. To avoid having anything that normally would not be active energized, I pop the hood when I stop and measure the voltage at the alternator terminal (which is connected directly to the battery positive terminal) and a good ground the next day. I have been concerned about the low voltage reading (12.4 to 12.5 volts) my battery has since I got the car. It has not changed even after a long trip where it is fully charged. Alternation reads ~14 volts. However I have not had a starting problem and went on vacation for 3 weeks and it started just fine when I returned. When I returned from the trip I drove about 30 miles, checked it the next day and it was still 12.4 volts! I checked my digital volt meter with one at a battery store and both read 12.9 volts for a battery on the shelf. I have stopped being concerned, just curious.
 

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Agree, in addition after the car has been running there is a higher voltage surface charge on the battery, which depletes over time. I measure battery voltage after the car has been sitting 12 plus hours. To avoid having anything that normally would not be active energized, I pop the hood when I stop and measure the voltage at the alternator terminal (which is connected directly to the battery positive terminal) and a good ground the next day. I have been concerned about the low voltage reading (12.4 to 12.5 volts) my battery has since I got the car. It has not changed even after a long trip where it is fully charged. Alternation reads ~14 volts. However I have not had a starting problem and went on vacation for 3 weeks and it started just fine when I returned. When I returned from the trip I drove about 30 miles, checked it the next day and it was still 12.4 volts! I checked my digital volt meter with one at a battery store and both read 12.9 volts for a battery on the shelf. I have stopped being concerned, just curious.
My initial thought was voltage drop due to the 10+ feet of cable between the battery and alternator but doing some calculations that only accounts for about a .01 volt drop. Have you checked at the battery itself to compare?
 

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I have a C7 which is also encountering the erratic voltage issues. I can be going down the highway and the voltage will go down to 12.6 and stay there for along time. Then it will go back to 14.3-14.4.
Any ideas,
I have 7000 miles on the car and this just started.
 

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This is the same charge system used in most of the GM vehicles. The charge current is monitored via the computer, and the alternator has several levels of output depending on several factors. If the battery is fully charged, and very little accessories are being used, the output of the alternator slowly turns off, which in turn improves fuel economy due to less load put on engine. I believe there is 8 different levels of output voltage used on the new alternator systems. I had noticed the same symptoms on my 07 Avalanche, which ended up being completely normal. If at any point your battery voltage drops below 12 volts, then I recommend having a modern load test put on to check it out.
 

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My initial thought was voltage drop due to the 10+ feet of cable between the battery and alternator but doing some calculations that only accounts for about a .01 volt drop. Have you checked at the battery itself to compare?
Did check at the battery when I installed my radar detector mount to be sure the connections were tight. They were. I use a high quality digital meter that takes extremely small current draw so there is no voltage drop when the car is not running. When I brought to the dealer for a rear fluid check they said it was fine. But they never even uncovered the floor rug so didn’t check the batty by removal and putting on load bank. Didn’t think they would, easier to say its fine!!
I believe it is the battery, probably a weak cell but so far, after a year, it has started fine, even after a 2 ½ week vacation. I have stopped being concerned and just curious. Also been looking to see what glass mat battery will fit so when I have to replace it. The large circuit board that attaches to the left battery post means you have to must the same post arrangement. Optima posts are not in the same location.
 

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My charts ive always used show 12.6 is a full charge after surface charge is removed.
Agree Glen, if it was 12.6, I would not have been concerned, although for a typical lead acid battery 12.7 is more typical. With my consistent reading of 12.4 the charts show only 70 to 75% charge. That is why I bought the Chevy type charger initially and checked the meter at the battery store with their meter and they both read 12.8 volts as I recall. Have a couple of other low cost digital meters and they read about the same. Also I never see the charging voltage drop below about 14 volts so believe the “car” thinks it needs to continue to charge it!
I am used to the Optima I have in my Street Rod and had put in my C6, which is higher, but that is due to their construction. As mentioned, I stopped being concerned and am now just curious and looking to what I’ll replace it with, when needed.
 

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Jerry; Why not make a point of getting the battery load tested (at Advance or other free spot) just to see if there is a weak cell, so you can go to your dealer with some confidence that there is a problem with the battery?
 
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