Go Back   Corvette Forum > C5 Corvettes, 1997 - 2004 > C5 Tech
Sign in using an external account
Register Forgot Password?
Register Albums Search Today's Posts Mark Forums Read FAQ
Search
C5 Tech
Corvette Tech/Performance: LS1 Corvette Technical Info, Internal Engine, External Engine, Tech Topics, Basic Tech, Maintenance, How to Remove & Replace Sponsored by
Karl Chevrolet

Welcome to Corvetteforum.com!
Welcome to Corvetteforum.com.

You are currently viewing our forum as a guest, which gives you limited access to view most discussions and access our other features. By joining our community, at no cost, you will have access to post topics, communicate privately with other members (PM), respond to polls, upload content and access many other special features. Registration is free, fast and simple, join Corvetteforum.com today!


Corvette Store
 
 
C6 Parts & Accessories
C5 Parts & Accessories
Wheels & Tires
Sponsored Ads
 
 
Vendor Directory
  
Reply
 
 
 
 
Thread Tools Search this Thread
Old 07-13-2006, 11:36 PM   #1
JC in XTC5
CF Senior Member
 
JC in XTC5's Avatar
 
Member Since: May 2000
Location: Southern NH
Default What's proper Battery Voltage

I'm thinking my battery is starting to go. I put a voltmeter on the battery with everything off, and it was only 12.2 and as low as 11.8. I believe a fully charged battery should be at about 13.

I've been having some hard starting problems where the car cranks a bit long before firing, or fires right up on the second try, and I'm thinking the lower than normal voltage is the reason since it could affect the sensor readings and PCM operation during cranking.

I plan to get an Optima Red Top this weekend, but wanted to check if anyone could confirm my suspicions.
JC in XTC5 is offline   Reply With Quote
Old 07-14-2006, 12:01 AM   #2
HollywoodFRC
CF Senior Member
 
HollywoodFRC's Avatar
 
Member Since: Jan 2006
Location: Hollywood Maryland
Default Check battery

Get a Volt Ohm meter. Drive the car to reach normal operating temperature. Park as normal. Hook up the meter and note voltage. Put meter up on lower windshield and gently close the hood to turn off underhood light. Check meter right before bed and in the morning. Voltage should not drop appreciably. I have an Optima Red top and it typically registers 12.54V when I park it and sometimes drops to 12.51 or 12.52 overnight, not much. For three months I've had the Red Top and no problems. Good luck.

HollywoodFRC is offline   Reply With Quote
Old 07-14-2006, 12:14 AM   #3
Oldvetter
CF Senior Member
 
Oldvetter's Avatar
 
Member Since: Feb 2002
Location: Waldorf MD
Default

From batterytender.com:

1. How can I tell if my battery is charged or not?

Lead acid batteries are made up of cells. Each cell is approximately 2 volts, so a 12-volt battery has 6 individual cells. It turns out that a fully charged 2-volt cell has a voltage of approximately 2.15 volts. Oddly enough, a fully discharged 2-volt cell has a voltage of 1.9 volts. Thatís only a difference of 0.25 volts on each cell from fully charged to fully discharged. So a 12-volt battery will measure at about 12.9 volts when itís fully charged and about 11.4 volts when it is fully discharged. Thatís a total of 1.5 volts that represents the full range of charge on a 12-volt battery. To make a good guess at how much charge your battery has left, you can assign a percentage of charge remaining that is directly proportional to the battery voltage. Letís see how we can do that. If the battery voltage is 12.15 volts, how much charge is left? Beginning with 11.4 volts representing no charge or 0% charge available, subtract 11.4 volts from the voltage that you read. So 12.15 Ė 11.4 = 0.75 volts. Since there are only 1.5 volts above 11.4 volts that represents the full range of charge, we can divide the difference that we just calculated by 1.5 volts to get the percentage of charge remaining. 0.75 volts / 1.5 volts = 0.5 or when expressed as a percentage, multiply by 100 and get 50%. Hereís the procedure written as a formula that is applicable to 12 Volt Batteries:

OPEN CIRCUIT BATTERY STATE OF CHARGE CALCULATION

% Charge = SOC

% Charge = ((Measured Battery Voltage Ė 11.4 volts) / 1.5 volts) x 100

Equation 1
That seems easy enough. So whatís the catch? In order for this formula to work, the battery must be in a rest state. In other words, the battery should not be supplying power to any type of load. The experts say that the battery should remain at rest for at least 24 hours to get an accurate measurement, but in a pinch a couple of hours are good enough to make a reasonable guess. Even if the battery is connected to a load, as long as the load current is less than 1% of the battery capacity in amp-hours, then this method is probably good enough in most cases. Itís all a matter of how accurate you want to be. If youíre a scientist or engineer trying to develop a battery powered product, then you probably want a more accurate measurement than if youíre going fishing for the weekend and you just want to know if you need to take the time to charge your battery before you use it. There is one more thing to keep in mind. The only way to be absolutely sure that your battery is fully charged is to do a load test. It is best to have the battery dealer do this for you. We only mention it here because it is possible for a battery to indicate a good voltage, but then immediately when you try to use it, it acts like itís dead. This doesnít happen very often, but itís good to know that it is a possibility.
Oldvetter is offline   Reply With Quote
Old 07-14-2006, 12:54 AM   #4
CraZee ZO6
CF Senior Member
 
CraZee ZO6's Avatar
 
Member Since: Jan 2004
Location: St. james NY
Send a message via AIM to CraZee ZO6
Default

Ive seen mine vary from 13.8 to 14.1.......
CraZee ZO6 is offline   Reply With Quote
Old 07-14-2006, 01:38 AM   #5
JC in XTC5
CF Senior Member
 
JC in XTC5's Avatar
 
Member Since: May 2000
Location: Southern NH
Default

Quote:
Originally Posted by CraZee ZO6
Ive seen mine vary from 13.8 to 14.1.......
That's the alternator voltage with the car running. I'm looking for the battery voltage with the car off.

I'll re-measure tomorrow to see if it drops below 12 overnight as I suspect.
JC in XTC5 is offline   Reply With Quote
Old 07-14-2006, 03:00 AM   #6
GrayC5
CF Senior Member
 
GrayC5's Avatar
 
Member Since: Nov 2003
Location: Mustang OK
Default

Taking a voltage reading at the battery terminals will only tell you the state of charge of the battery. In order to get an accurate voltage reading, you need to use an accurate digital volt-ohm meter (DVOM). Too, you will first need to remove any surface charge of the battery and the temperature of the electrolyte will need to be taken into consideration. To completely determine the condition of the battery, other tests are required. The following link contains some very good information on the proper way to test an automotive battery. A State-of-Charge chart is also included there:

CAR BATTERY FREQUENTLY ASKED QUESTIONS

HTH

Last edited by GrayC5; 07-14-2006 at 03:15 AM.
GrayC5 is offline   Reply With Quote
Old 07-14-2006, 12:37 PM   #7
JC in XTC5
CF Senior Member
 
JC in XTC5's Avatar
 
Member Since: May 2000
Location: Southern NH
Default

Quote:
Originally Posted by GrayC5
Taking a voltage reading at the battery terminals will only tell you the state of charge of the battery. In order to get an accurate voltage reading, you need to use an accurate digital volt-ohm meter (DVOM). Too, you will first need to remove any surface charge of the battery and the temperature of the electrolyte will need to be taken into consideration. To completely determine the condition of the battery, other tests are required. The following link contains some very good information on the proper way to test an automotive battery. A State-of-Charge chart is also included there:

CAR BATTERY FREQUENTLY ASKED QUESTIONS

HTH

Yes, I've been using a DVOM to take my readings. This morning it was at 12.14V after sitting overnight and leaving the hood unlatched so I wouldn't activate any load (keyless) before the reading, which is less than 50% from the chart on the link you posted. I drove to work this morning (~ 20 minutes) and now 3 hours later I'm taking a reading (90F outdoor temp). Battery reads 12.30V, which is still barely above 50%.

I must mention that this battery as the AC Delco AGM (78P-7YR) that was installed about 5 years ago. The sides of the case are bulging a bit which I understand is normal for AGMs due to the positive pressure they operate under.

I had put my battery tender on it earlier in the week to see if it would fully charge, and the next morning my tender was completely dead (don't know if it's just coincidence or another indication that the battery is going). Later that day the battery was at 12.50V which is still not great assuming the tender was able to get some charging done before it died.

I guess the safest thing to do is just replace it at this point.
JC in XTC5 is offline   Reply With Quote
Old 07-14-2006, 11:38 PM   #8
patton
CF Senior Member
St. Jude Donor '09
 
patton's Avatar
 
Member Since: Jun 2004
Location: trenton nj
Default

5 yrs old ? that batt was going down hill 2 yrs ago may be over kill but i pop a new batt in ever 3 to 4 yrs . i like top of the line interstates
patton is offline   Reply With Quote
Old 07-15-2006, 08:44 AM   #9
Tact
Law Dawg Moderator
St. Jude Donor '05-'06-'07-'08-'09-'10-'11-'12-'13-'14
 
Tact's Avatar
 
Member Since: Jan 2005
Location: Eads, Tennessee

Default

Quote:
Originally Posted by JC in XTC5
Yes, I've been using a DVOM to take my readings. This morning it was at 12.14V after sitting overnight and leaving the hood unlatched so I wouldn't activate any load (keyless) before the reading, which is less than 50% from the chart on the link you posted. I drove to work this morning (~ 20 minutes) and now 3 hours later I'm taking a reading (90F outdoor temp). Battery reads 12.30V, which is still barely above 50%.

I must mention that this battery as the AC Delco AGM (78P-7YR) that was installed about 5 years ago. The sides of the case are bulging a bit which I understand is normal for AGMs due to the positive pressure they operate under.

I had put my battery tender on it earlier in the week to see if it would fully charge, and the next morning my tender was completely dead (don't know if it's just coincidence or another indication that the battery is going). Later that day the battery was at 12.50V which is still not great assuming the tender was able to get some charging done before it died.

I guess the safest thing to do is just replace it at this point.

I haven't seen many batteries lasting much longer than yours. Also with your readings it appears the battery is on it's last leg. I've always tested my batteries and felt assured they were OK with a reading near 12.6. My battery is only a couple of years old and only shows a reading of 12.3, but it sits a long time between drives. I'm thinking of switching to a jell battery , mainly for piece of mind.
Tact is offline   Reply With Quote
Old 07-15-2006, 11:57 PM   #10
JC in XTC5
CF Senior Member
 
JC in XTC5's Avatar
 
Member Since: May 2000
Location: Southern NH
Default

Thanks Guys.

Well I just bought an Exide Orbital battery today. They're supposed to be great AGM batteries that can withstand deep cycle use. $129 at NTB.
JC in XTC5 is offline   Reply With Quote
Old 07-15-2006, 11:57 PM
 
Go Back   Corvette Forum > C5 Corvettes, 1997 - 2004 > C5 Tech
Reload this Page What's proper Battery Voltage
 
 
 
Reply

Tags
battery, c5, proper, voltage


Thread Tools Search this Thread
Search this Thread:

Click for Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Weights, measurements, ratios, strengths, etc leaftye C5 Tech 252 02-02-2014 12:23 PM
Does anyone have Andy's Head/Cam special? MagRed01Atty C5 Tech 17 05-19-2004 08:01 PM
Trivia Time! Urban/Rural Legends re Battery Storage on Concrete Floors... paul 74 C3 Tech/Performance 21 11-03-2002 05:38 PM
Can a low battery cause poor idle and rough running? Fevre C3 Tech/Performance 24 06-24-2002 04:37 AM
I have just about had it! - What would you do? bparker C5 Tech 30 11-12-2001 11:33 AM
Is there a bypass for GM's Column Lock Fix? Just J C5 Tech 12 09-20-2001 11:31 AM


All times are GMT -4. The time now is 12:24 PM.


Emails & Password Backup

Search Engine Friendly URLs by vBSEO 3.5.2