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I think some of those SOC numbers are "deduced" after the car has monitored charge for a while. The same nonsense that the oil level uses, requiring you to drive for so many hours before it will reset itself and just read the level.
To actually measure SOC they would have to know the rated capacity, and then do an internal impedance test, or a load test. Audi doesn't do either, they're just counting coulombs in and out and pretending they know something more.
If you had another DC power source hooked up, and it was slightly higher than battery voltage? The car might have the wrong number "stuck in its craw", so to speak.
Thanks everyone for the informative posts on the Q5 battery replacement!
For a while now, my radar detector had been powering down due to "Low Voltage" and recently, won't even power on.
Since the battery is over 5 years old, figured it was time for a battery change and asked dealer to check battery health at last service.
They reported back that it was fine but I could proactively replace it for $855 if I wanted to. Yikes!
After reading up on these forums, decided I'd pick up a battery charger for about $100, and a new battery for about $200 and come out $555 ahead (already have Ross-Tech VCDS cable).
So, went to O'reilly Auto Parts to pick up new battery and since they offer free battery testing, had them test it and the test showed that the battery was fine, too! Huh??
Anyway, after charging battery to full overnight using C-Tek charger, car showed 55 Ah "Battery capacity (actual/available)" this morning and that is already down to 48 Ah after driving around a bit today. I'm expecting that number indicates that battery is less than 50% of capacity compared to new (105Ah)?
I figure the higher CCA and CA values can only be good?
Plan is to charge up the new battery to full using CTEK charger, then connect CTEK in Supply mode to the car, swap out battery, and just increment serial # by 1 in VCDS to let car know it has a new battery.
Offhand, yes, that sounds good. $800 at the dealership, huh? Well, that does include free coffee, snacks, and a car wash...
I called parts department separately for just the battery and it was about $450 with tax... So, $400 for taking out the old battery, putting in a new one, and recoding it? And I guess they'd probably give me a loaner car, too...? =)
No no. Only a $200 diagnostic fee to make sure the battery IS the problem, and then another $200 programming fee to tell the car what the new battery's make and serial number are. Which apparently makes no difference at all to anything--except, it makes it harder for you to put someone else's old battery in your car and claim "But you just put this in six months ago and it is dying!" for a warranty scam.
That, and the new programming resets the "wake me up when the battery is getting old?" timer routine, which is pretty much useless anyway. They generate all that sensor information, and don't use it for charge management. Almost as high-tech as a Ford Pinto.(sigh)
The only true way to measure how good your battery is, is to charge it up with your CTEK charger and then test it with a carbon pile load tester set at one half oF the rated CCA.
That Group 20 capacity remaining is a bogus number as one would need to fully charge the battery to 100% and then fully discharge the battery with a fixed load recording the time that it takes. The Audi power management system doesn't have that capability.
BTW your old battery 580 A "DIN" equates to 1000 CCA SAE, So your 2 batteries are very similar in performance.
Last edited by Bob Petruska; 10-09-2018 at 09:14 PM.
Bob-
Carbon pile load testers still work and work well. But they belong with your father's Oldsmobile.
For the past 20 years or so, shops have been using electronic meters that measure the batteries internal resistance to AC frequncy (not the simple resistance from an ohmeter) and reporting on their condition based on that. Go to any battery distributor, go to any WalMart auto center, call any AAA battery replacement service, they all use the electronic testers.
And, funny thing, IIRC the VCDS display shows that the Audi is reading and reporting that same figure--just not doing anything with it, according to Audi.
In the down and dirty world, every battery maker and most charging system makers will tell you that you only need a (calibrated) DC voltmeter to tell battery condition. And that's been done for 40 years now. You start with a fully charged battery, and you knock off the float charge by putting on a load (headlight) for 2-3 minutes, then let the battery sit a few more minutes. Or, you can just let the fully charged battery sit overnight, until the electrolyte has had a chance to circulate and equalize.
Then you just measure the voltage. A typical new battery at 100% capacity is 12.6 volts (some may be 12.7, there's always a spec sheet to say) and the effective capacity is 10% less per 0.1V that the voltage has dropped. So, at 12.1 volts you are looking at a 50% capacity battery. It really is that simple, even if there is still some imprecision in the result. The carbon pile test is not needed.
Most of the folks who say "Oh that doesn't work" are just using uncalibrated multimeters. I've seen a "good" one that was simply old (they all shift as they age) that was wrong by 0.2 volts--which would be a 20% error in battery capacity. And a brand new one from Horror Freight, their red $7.95 "free with any purchase" model, that was off by a whopping 0.4v right out of the box. That's a 40% state of charge error.
But calibrated, or at least compared to a "known good" voltage, they work just fine.
Why Audi bothers to make the more sophisticated test and then throws out the data...Hey, if you'd helped me take hostages, we might have found out by now.
Bob-
Carbon pile load testers still work and work well. But they belong with your father's Oldsmobile.
For the past 20 years or so, shops have been using electronic meters that measure the batteries internal resistance to AC frequncy (not the simple resistance from an ohmeter) and reporting on their condition based on that. Go to any battery distributor, go to any WalMart auto center, call any AAA battery replacement service, they all use the electronic testers.
And, funny thing, IIRC the VCDS display shows that the Audi is reading and reporting that same figure--just not doing anything with it, according to Audi.
In the down and dirty world, every battery maker and most charging system makers will tell you that you only need a (calibrated) DC voltmeter to tell battery condition. And that's been done for 40 years now. You start with a fully charged battery, and you knock off the float charge by putting on a load (headlight) for 2-3 minutes, then let the battery sit a few more minutes. Or, you can just let the fully charged battery sit overnight, until the electrolyte has had a chance to circulate and equalize.
Then you just measure the voltage. A typical new battery at 100% capacity is 12.6 volts (some may be 12.7, there's always a spec sheet to say) and the effective capacity is 10% less per 0.1V that the voltage has dropped. So, at 12.1 volts you are looking at a 50% capacity battery. It really is that simple, even if there is still some imprecision in the result. The carbon pile test is not needed.
Most of the folks who say "Oh that doesn't work" are just using uncalibrated multimeters. I've seen a "good" one that was simply old (they all shift as they age) that was wrong by 0.2 volts--which would be a 20% error in battery capacity. And a brand new one from Horror Freight, their red $7.95 "free with any purchase" model, that was off by a whopping 0.4v right out of the box. That's a 40% state of charge error.
But calibrated, or at least compared to a "known good" voltage, they work just fine.
Why Audi bothers to make the more sophisticated test and then throws out the data...Hey, if you'd helped me take hostages, we might have found out by now.
Well I respectfully disagree with a lot of what you state here..........
1. Carbon Pile Load testers just don't lie. 2 weeks ago my father's battery died. I charge it up, disconnected from the car electrical system, with the CTEK charger . 3 days later the battery was down to 12.1 volts. Charged it up again Solar electronic conductance tester indicated that the battery was fine 12.7V and the CCA was 752 A, this is a 700 CCA rated battery. Put the carbon pile load tester on it and it took the battery voltage down to 11.92V in a few seconds, resulted in 98 CCA. The battery was from AA, 2 years old , with a 3 year replacement warranty. Took the battery back to AA, they said they need to charge it up first and run the conductance tester on it, before warranty replacement They did so and it passed with flying colors, 12.8v 732 CCA. They said no warranty replacement. I said that I will be back tomorrow and we will test again, 24 hours later 12.2 volts 152 CCA, battery replaced, so much for electronic conductance testers at AA, Walmart, etc.
2. Charged up the new replacement battery off the car, 13.1 volts, put the carbon pile load on it for 2-3 seconds to bleed surface charge, then 12.8V 742 CCA, using the Solar conductance tester. Hooked the battery up to the car electrical system, test again using the Solar, 12.8V, but now dropped to 420 CCA!!! I said the car's electrical system in parallel across the battery is affecting the Solar conductance reading (EE101). Contacted Solar's tech support and had a very good discussion. The way an electronic conductance tester determines the CCA reading is by programing the battery rated CCA into the tester, conductance is measured, it then uses a look up table (LUT) to match preprogrammed conductance measurements versus projected CCA from data gathered by measuring many batteries in the lab from various battery manufacturers and averaged. That's an ok workflow, but not very accurate if the car's electrical system is going to affect conductance measurements.
I'll use a carbon pile load tester from here on out to determine good or bad batteries.
3. You can't determine battery condition by voltage measurements alone. You could have an old battery that has 90% of it's capacity gone due to plate sulfation, and it will still charge to 100% to 12.8V, and drop in voltage just as a new battery would, just quicker. It just would have very little AH capacity/CCA. It just charge swings in that 0 to 10% capacity range remaining, I saw that in my father's battery, and many other's in my life.
Last edited by Bob Petruska; 10-10-2018 at 05:11 PM.
Well I respectfully disagree with a lot of what you state here..........
1. Carbon Pile Load testers just don't lie. 2 weeks ago my father's battery died. I charge it up, disconnected from the car electrical system, with the CTEK charger . 3 days later the battery was down to 12.1 volts. Charged it up again Solar electronic conductance tester indicated that the battery was fine 12.7V and the CCA was 752 A, this is a 700 CCA rated battery. Put the carbon pile load tester on it and it took the battery voltage down to 11.92V in a few seconds, resulted in 98 CCA. The battery was from AA, 2 years old , with a 3 year replacement warranty. Took the battery back to AA, they said they need to charge it up first and run the conductance tester on it, before warranty replacement They did so and it passed with flying colors, 12.8v 732 CCA. They said no warranty replacement. I said that I will be back tomorrow and we will test again, 24 hours later 12.2 volts 152 CCA, battery replaced, so much for electronic conductance testers at AA, Walmart, etc.
2. Charged up the new replacement battery off the car, 13.1 volts, put the carbon pile load on it for 2-3 seconds to bleed surface charge, then 12.8V 742 CCA, using the Solar conductance tester. Hooked the battery up to the car electrical system, test again using the Solar, 12.8V, but now dropped to 420 CCA!!! I said the car's electrical system in parallel across the battery is affecting the Solar conductance reading (EE101). Contacted Solar's tech support and had a very good discussion. The way an electronic conductance tester determines the CCA reading is by programing the battery rated CCA into the tester, conductance is measured, it then uses a look up table (LUT) to match preprogrammed conductance measurements versus projected CCA from data gathered by measuring many batteries in the lab from various battery manufacturers and averaged. That's an ok workflow, but not very accurate if the car's electrical system is going to affect conductance measurements.
I'll use a carbon pile load tester from here on out to determine good or bad batteries.
3. You can't determine battery condition by voltage measurements alone. You could have an old battery that has 90% of it's capacity gone due to plate sulfation, and it will still charge to 100% to 12.8V, and drop in voltage just as a new battery would, just quicker. It just would have very little AH capacity/CCA. It just charge swings in that 0 to 10% capacity range remaining, I saw that in my father's battery, and many other's in my life.
I realize that this is mostly friendly banter between 2 guys but for some innocent/not too knowledgeable owner (not a garage) who just wants the minimum effort, here are some practical tips:
Any voltmeter that is repeatable will do as a test instrument if you repeat measurements and keep track. Battery full charge charge value depends on temperature. Easy to look up but winter values are about 0.3-0.4V lower from memory. In marginal situations a battery refusing to crank may sometimes be coaxed back to life by moving it to a warm place for a short time. So if cranking time is increasing do a few measurements to see how the battery voltage is trending. Replace battery if it is a definite dying trend. Little payback in procrastinating e.g. get 5 year vs 4 year life vs a costly/unpleasant experience on the road.
I realize that this is mostly friendly banter between 2 guys but for some innocent/not too knowledgeable owner (not a garage) who just wants the minimum effort, here are some practical tips:
Any voltmeter that is repeatable will do as a test instrument if you repeat measurements and keep track. Battery full charge charge value depends on temperature. Easy to look up but winter values are about 0.3-0.4V lower from memory. In marginal situations a battery refusing to crank may sometimes be coaxed back to life by moving it to a warm place for a short time. So if cranking time is increasing do a few measurements to see how the battery voltage is trending. Replace battery if it is a definite dying trend. Little payback in procrastinating e.g. get 5 year vs 4 year life vs a costly/unpleasant experience on the road.
Yep,, we just like "battery talk"!
What you say is correct, any volt meter will let you know how much the battery is "charged", but it will not tell you the remaining "capacity" of that battery. Capacity (rated Ah) decreases as the battery ages, but will still charge to 100%. There is a major difference between the percentage of charge and capacity.
08-20-2018, 12:44 PM
