Last weekend when I was going through my "service column lock" fiasco,while preparing to do the CLB install,I was checking a few things out to rule them out as a cause.One of them was I took a voltage meter and checked the voltage at the terminals. The car is driven almost daily,and had been on a short drive prior to the problem. It always starts and runs fine,, but I was kind of surprised to get a reading of 12.16 volts !! Seems a little low to me. When running the terminal voltage was 14.45 which seems fine. I am aware that low voltage can cause a lot of problems. Does it sound like I'm due for a new battery?? Don't want to throw money away,,but I don't want to cheap out and wind up with problems either!!

 

You're fine.

 

If the terminal voltage across the battery is only 12.16 volts after it has sat one day or less then that tells me your battery is getting weak. It should hold above 12.5 ~ 12.6 for at least a few days or more.

Do this. After driving the car let it sit one hour. Measure the terminal voltage and record. If the car isn't planned to be driven for a while, take another terminal voltage measurement every 24 hrs and record. If the battery voltage drops below 12 volts in a matter of a couple of days then the battery is getting weak or you have some excessive parasitic current draw.

Your charging voltage looks good.

 

Would you change the battery for .2 volt? Just keep an eye on the DIC occasionally before you start the car to see if it's really dropping or if that's just what it is. Mine often is below 12 volts when it sits a while, but it always starts and runs fine.

 

Same here. My DIC will often display 11.6 - 11.9 on the DIC just before start-up, but it's also over 5 years old too and getting long in the tooth.

 

Go do the research. A healthy battery should maintain a voltage of 12.5 ~ 12.6 volts for many days. If it drops below 12 volts after sitting a few days then it's starting to degrade pretty badly and will fail later down the road.

If someone wants to run on a weak battery then fine, and if driven every day will probably last awhile. I'm just stating the facts about batteries ... take the data and make your own decision to swap it out or not.

And BTW, it's more than 0.2 volts ... more like 0.5 volt difference for the OP.

 

The DIC voltage is always lower than the actual battery terminal voltage by 0.3 ~ 0.5 volts.

 

Thanks for the input,,will check a few more times. The 12.16 was a AT THE TERMINALS,,checked with a volt meter. I DO want to keep on top of it as I do drive it through the winter. The reading was after a short 5 minute or so drive and the hood had been up for a while. Was unsure what a battery at rest should have,,and was also unsure about "the problem level" for voltage with C5s!! Thanks again!!

 

Zee06 gives some good advice. If the battery is at 12.16 volts right after a drive, it's on it's way out. Closer to 12.5 or 12.6 volts is normal. In my experience, anything under 12.0 volts and you'll start having trouble starting and other symptoms.

 

Well of course it is. That's why I specified DIC in my post instead of at the battery.

 

I am going to keep CLOSE tabs on it!!(will carry the voltage meter with me) If this is not an anomaly,I WILL be putting a NEW battery SOON!! thanks again for all the input/info..

 

Hi, all the advice you got here is mostly good advice. The thing you have to keep in mind is that taking a reading with the battery cables hooked up will not give a true soc(state of charge), reading. Testing in the car after the hood light is on for a while, and only being driven 5 minutes before hand is not really going to tell you much, and the reading you got is not abnormal under that circumstance, especially with a battery that is not maintained at full charge. Also a load test is a better way to test if the battery is able to hold a good charge under load. Most places like pep boys, advance, autozone, will do this for you at no charge.
To get a true soc reading, you have to charge the battery full, then wait 4 to 8 hours and then test across the terminals. This should be done with the batt disconnected from the car.
The following readings will be evident on a lead acid water flooded battery at 80 degrees. AGM will read very slightly higher.

Good Luck
=================================
Test the battery at room temperature. Allow 4-8 hour of rest after charge or discharge.
12.65V 100%
12.45V 75%
12.24V 50%
12.06V 25%
11.89V or less Discharged

 

... if your hood light and some of the computers were not fully 'asleep' when you tested the voltage across the battery then there was probably enough of a current draw to bring the terminal voltage down some.

You can get a true terminal voltage without taking the battery out of the car or unhooking the battery cables. This is how I do it. Lift the hood just enough so it will stay lifted by its self ... at this position the hood light should still be off. Put a battery tender charger or similar on the battery and let it fully charge. Remove the charger and then come back 4 or 5 hrs later and measure the voltage. The only current draw should be the 18 ~ 20 mA of normal 'parisitic' draw which is much too low to effect the terminal voltage. This can also be done after a drive ... simply pop the hood and lift it to the position it will remain open by its self. Then come back 4 or 5 hrs later and measure the voltage. Do not open the hood or doors, as this will energize the computers and draw battery current. Just make the voltage measurement without touching anything else.

Every year during the car's hibernation I do this test, and measure/record the voltage every day to see how the terminal voltage drops by plotting the data. I can instantly see if the battery is going south. Like I said earlier, if the terminal voltage drops below 12.0 volts in a day or two then it's not holding a charge and is pretty well on it's way out.

 

The info I saw for a 12v battery 'state of charge' follows. The state of charge voltage is approximate, and you'll probably see differences in the data, but the trend is similar.

100% -- 12.7 volts
75% -- 12.4 volts
50% -- 12.1 volts
25% -- 11.7 volts
0% -- 10.5 volts (discharged)

 

Thanks again guys,,now I have some hard #s and how to check them. As you can guess, I'm new to to diagnosing the new electronic age stuff!! I started helping over 50 years ago,,and have been DIY for over 45. Did my first rebuild over 43years ago,,,,but I'm a real noobie with all the computer controlled stuff!!! Running through all the codes,,I might have been looking at Chinese symbols!! Will have to try the hood trick to let the computer go to sleep as I like to keep track of mileage(an OLD habit I have with all my vehicles since my first car,old VWs didn't have gas gauges) Disconnecting the battery clears trip miles and averages and so on.

 

Sorry for the noob question. But at what point should you replace the battery?

 

My opinion would be if it won't hold better than between 50 and 75% with regular use and you are charging up to snuff I would be seriously looking. Turnsout mine had just run down,,Used ZeeOsix's test after a drive and had readings of12.93 at 4hrs and12.84 at 20hrs. For reference the alternator was putting out 14.4 at the battery when running!

 

... I'd say if the battery falls below 12.4 volts (75% charge) in less than 3 or 4 days then the battery is getting ready to die.

Itzza427 - sounds like all is good with your battery and charging system.

 

After a 50 minute drive, I let the car sit for the last four hours. The alternator was running at 14.2 amps at first, then went down to 13.7 by the end of the drive. The hood was raised without the light coming on, giving me access to the battery. I just put a meter across the terminals without lifting the cables. I have a reading of 12.81 VDC after four hours. After 16 hours she's holding at 12.74 VDC. So far so good.

volts hours

12.81 4
12.74 16
12.71 24
12.65 52

Looks like its holding up pretty good. I don't think I have a battery problem?

 

I dug up some battery voltage measurements I did earlier this year when my Zee was in hibernation. The battery is an Optima Red Top that is about 3 years old now. I did this same test when the battery was basically new for a baseline.

I first charged it up fully with a Battery Tender Plus. Here are the terminal voltage measurements after the full charge and with the hood partially up so the under hood light stays off and all computers are in 'sleep mode'. T is the time duration after removing the Battery Tender after a full charge. This is how a healthy battery would discharge while in the car with only the normal 20 mA current draw is on the battery.

T=1 hr -- V=12.60
T=1 day -- V=12.56
T=3 days -- V=12.52
T= 5 days -- V=12.48
T=9 days -- V=12.38
T=15 days -- V=12.38
T=17 days -- V=12.25
T= 21 days -- V=12.20

Below is the same terminal voltage test on an Optima Red Top battery that went bad on me when it was only about 4 months old. At first I thought it might be caused by excessive parasitic current draw, but I verified the current draw was 18~20 mA which is the normal level when all the computers on the car are in 'sleep mode'.

T= 0 hrs -- V=12.40
T=3 hrs -- V=12.30
T=17 hrs -- V=12.18 (you can see it's self discharging fast!)
T=27 hrs -- V=12.04
T=31 hrs -- V=11.95
T=51 hrs -- V=11.25
T=70 hrs -- V=11.0

This battery had self discharged to below 25% capacity in about 3 days. Obviously defective. Optima gave me a new battery under warranty and the 2nd one has been good for ~3 years now.