The battery went dead on my C6, 2007 Corvette. Had a new battery installed yesterday. Before the battery went, the voltage always read 14.6. After the new battery was installed the
Voltage read 14.2. Today it is 13.8, seems I am losing voltage. Could something be draining my battery?

 

13.8 sounds right, when are you checking it?

If you live near me, stop by, I have a bunch of battery test equipment (I retired from a battery manufacturer).

 

That's the system voltage being generated by the alternator...it is not the battery voltage. As long as the system voltage stays above about 13.2 with the engine running, all is fine. Lots of factors affect this voltage, even temperature.

 

Thanks so much for replying, I am relieved, as a Vette owner, I get a little paranoid!

Georgiagirl20

 

Thanks for your reply. I was basing the 14.6 on what it was before the battery went dead. However, another person replied to my post and said many factors could affect the way the voltage is registering and as long as it above 13.2 when the motor is running, I am okay. I feel relieved because I get a little anxious about my Vette when I think something is not quite right. I am afraid you are too far a way for me to stop by, you are in Wisconsin (WI) I believe and I am in Virginia quite a distance! Appreciate the invite though!

Georgiagirl20

 

sounds normal, like cclive said this is the voltage generated by the alternator and not that of the battery, probably it was working harder to charge the old battery which was having difficulty retaining a charge

 

Thanks!

 

although I would be concerned at 13.2 since I would consider that low unless that battery was overcharged and the alternator was idling. I'd like to be more in the 13.6 range with a new fully charged battery. 14.6 was working very hard to keep a bad battery up. 14.2 is working on a good still slightly discharged battery. Right after starting that would be very normal.

BTW, I bought a new battery last month from Autozone although I always recommend Interstate because Interstate rotates their batteries every 30 days so you don't get one that has gone dead on the shelf. When I got it home to install, the Autozone battery was stone cold dead. That's the last time I don't take my own advice.

 

There is a date code on the battery and my bet is that people kept taking the one behind the one bought because of age. The Interstate and Autozone batteries are identical inside if they have the same ratings.

 

So why do I consistently see 14.5-14.6 when, I start up and drive for a while, my car when it has been on a battery tender?

Supposedly the tender is maintaining a above 80% charge, green light steady.

I always thought that the 14.5 reading meant that the alternator was working like it should. It will stay at this voltage during long drives when the battery should be fully charged, one would think.

 

Before I got my C6, I had a C5 with a key start and you could check the BATTERY voltage by turning the key on but not engaging the starter, I don't know if the C6 has this feature, Anybody ??

 

That is possible with the C6 by putting the car into 'ignition on'...the equivalent of turning on the key in an older car without starting it. It is not an accurate reading of the battery voltage though because all the computer systems in the car are awakened when this happens, so there is a significant load put on the battery while reading the voltage on the DIC.

 

This thread is one reason I love this forum. There are so many knowledgeable people willing to share their knowledge like in this thread. I had some of the same concerns about my voltage readout on my car, but I never got around to asking here on the forum. Now I know thanks to reading this thread!

 

I experienced the same issues as you but turn out that my alternator was on the outs.

Rather than buying a rebuilt Alt from the local parts store, I took it to my local Alt repair shop, had it rebuilt with no issues.

Cost is about the same as buying a rebuilt but worry free.

 

Thanks for replying. Today I drove the corvette and the voltage was 14.2. The car seems to be running fine and the only thing I have to do now is have the rear differential fluid replaced as part of my 100,000 mile factory
scheduled check up.

 

Did you drive it for a while and warm it up fully? The voltage after warm up would be more important to me than the voltage right after startup.

 

My understanding, and observation, is actually the opposite. When a charger/alternator first starts charging a discharged battery, the voltage starts out low. As the battery becomes more fully charged, the measured voltage increases. A reading of 13.6 would indicate a battery that is more discharged than one reading 14.2, assuming the alternator in both cases is working correctly and putting out around 14.7 volts unloaded.

 

Thanks for your reply. Car is starting up right away, drove it today and the voltage on the dashboard read 14.2. Everything appear to be fine. Thanks for all the replies.

 

Charging a lead acid battery isn't as easy today as it was 50 years ago. 30 years ago you would be right. The voltage would start low and increase as you got toward 100% charge because the voltage regulator was essentially just an on off switch and the generator/alternator was doing all it could when on and then nothing when off. When we started getting solid state regulators it didn't change much except we started controlling the current output of the alternator a little to maintain a more constant voltage. Then we get to the computer control the C6 has. The Engine Control Module (ECM) is what controls the charging in the C6 and, by talking to the Body Control Module (BCM) it knows a lot more about what the battery needs than just simply looking at the voltage and current. Just watch the voltage after starting when it has been on a tender. The voltage will start high and then decrease over the next 15 minutes or so as the battery is recharged following the startup discharge. The ECM knows it just started the car and needs to be recharged fast because you might stop at the grocery soon and need another start. But if you keep driving it gets the battery back up and so reduces the voltage and current to the battery.

But you are correct when the battery gets so discharged that the ECM runs the alternator as hard as it can. At that point we are back to the way it worked 50 years ago. The battery is down and the alternator is full on. Voltage is low because the alternator is pumping all the current it can into a dead battery. As the battery charges the voltage rises until the ECM can start getting all it wants and the voltage will hold constant or start decreasing as the battery comes up toward full charge.

 

This article should answer all your questions regarding alternator and battery charging voltages.

While there is no question that variances in lead acid battery and alternator design, operating temperatures, and wiring condition, will effect voltages, this article will put you in the ball park with easily understood explanations.

http://www.w8ji.com/battery_and_charging_system.htm