An intermittent issue with the dying battery; chemical or plate shorting or...? *NM*

The 8-year old battery in my audi has been the battery from heaven. After 8 years, even if i left it for 2 weeks untouched, it would fire eagerly up.

Until this morning. Oddly, the car was driven extensively on the highway this week - so it had a great charge. Solenoid click. Jumped easily, took a charge but would lose voltage with time (trued up to 2 hours). When i started it the voltage dropped from 12 1/2V to < 8. Normally it drops to > 10V, so it is dying.

Yet it happened so fast! I took some current draw readings at the battery, with the key off and out of the ignition - nothing on, no bulbs. ~400mA. Seems like a lot - 10A-H per day. 5W. My 2000 boxster draws ~ 100mA. I did not have time to pull every fuse and observe the result, but i pulled quite a few with only minor results - no big winner.

Is this normal for cars with lots of electronic doo-dads? In its day (2002) the S6 avant was Audi's hot rod and technological showcase - it has everything that was a big deal back then.

Any insight?

Grant

Grant

gee-lenahan-at-gee-mail-dot-com



Edited 1 time(s). Last edit at 10/04/2014 04:07PM by grant. (view changes)

At 2:53--
StevenWright

Grant

gee-lenahan-at-gee-mail-dot-com

about an order of magnitude a lot of current draw.

Did you wait a few minutes, say 3 or even 5? Some cars can continue to draw some fairly high current even with the key out of the ignition and the car locked. My 996 for instance. The engine controller stays alive for 3 minutes after I shut off the engine and even after I lock the car. (The Boxster doesn't do this, but I have come across some other cars that do do this.) I do not recall what the 996's current draw is in this case but it well above the 40mA it is when it is checked later.

The high draw could also be due to internal battery failure of some kind. 8 year old battery? I think you got your money's worth and then some out of it. Put in a new battery and then check the current draw after immediate key off. Then check it 5 minutes later. If it is not down to under say 50mA then you have a sneak power drain.

You have to be careful, too. With some cars just unlocking the thing causes the current draw to jump as a lot of electronics comes alive.

You need to be able to measure/view current draw without having to unlock the car or even open a door or a trunk lid.

Yes, its seems high to me too. The 986/'00 draws 100-130ma. The 986.'04 draws 125-160 ma.

With the old battery the audi drew ~390-430 ma. With the new battery, it drew 340-360 ma.

Did i wait > 5 minutes? Not sure. But after < 60 seconds it went from 2A to ~400 ma. I went and dealt wth a roast, returned and it was ~ 390. Seemed stable. car was open, lights fuse pulled.

I agree it seems hgih to me, or i wouldn't be posting ;-) especially since all the other measurements on the original battery indicate that it is i fact mort. The only question is whether something pushed it over the edge... like a hgih draw.

I have been F-ing with the EVAP system, but that's mostly vacuum hoses and the e-connections to the solenoids - not exactly complex stuff. And ,amazingly, mostly fixed.

So.. not the clear answer you wanted, but all i'm able to give.

I think it may be a big pig.

Grant

Grant

gee-lenahan-at-gee-mail-dot-com

Put in new battery. Hooked up positive, but not ground. Inserted ammeter in line with ground. At connection - 2A draw. After 30 sec 390 mA draw - lasted nearly 10 minutes, then fell to -- get this -- 2mA (obviously sleep mode). So why didn't it sleep before, with the old battery? Several possibilities:

1. i didn't wait long enough?
2. Something about the dying battery caused errors... but i somehow doubt this since it was 12.5V n0 load even after i took it out, so for low load, the car saw full voltage....

Anyway, now when i re-connect it it goes to ~ 2V for 20sec, then nearly immediately to 2mA.

i conclude all is well and it was nothing more than a battery.

I'm always worried when i've been F-ing around with the car and then something dies....but it appears to have been a coincidence.

Hopefully these readings will help others. I'll post if I learn anything more or contrary.

Grant

Grant

gee-lenahan-at-gee-mail-dot-com

I know a few things:

1. it went from very strong to very dead overnight, or over a couple of days at most.
2. when dead, under cranking, the voltage fall to < 8V
3. When under no or light load, the voltage remained > 12V (12.4ish)

I don't know the chemistry and mechanics of how cell's exactly short. If one truly shorted, the no-load voltage would be ~ 10V.
But a "soft short" of some kind could result in precisely what I'm seeing.

The fact that it failed so quickly suggests that one thing failed, not 6. So i would doubt that slow, uniform degradation of the plates is the issue.

Let the speculation begin.

Grant

Grant

gee-lenahan-at-gee-mail-dot-com

it has a high resistance to charging. If your battery is heavily sulfated this can foil the charging circuitry.

I would have tried desulfating the battery first. That might have solved the problem.

1. battery was not working OK, it was working great- could leave the car 3 weeks and it would crank up like a happy puppy. I must assume that sulfation occurs gradually, no?

2. Suddenly it goes nearly dead. Full charge at no-load, but < 8V cranking, and that wont last long.

Maybe. I didnt. Its gone. I'm happy.

Thanks anyway

Grant

Grant

gee-lenahan-at-gee-mail-dot-com

at which the charger is fooled into not charging the battery. From then on it's quickly downhill.

Normal battery wear is much more gradual than sulfation.

As I said, it is entirely possible you could have solved the problem without replacing the battery.

24 hours earlier? This is the DD, not some occasional use vehicle.

I admit i never really considered it, but that was due to the circumstances - they don't fit the pattern.

Grant

Grant

gee-lenahan-at-gee-mail-dot-com

Quote
grant
24 hours earlier? This is the DD, not some occasional use vehicle.

I admit i never really considered it, but that was due to the circumstances - they don't fit the pattern.

Grant

Depends.

Daily usage may not be sufficient and in fact could contribute to the condition.

Even if the car is driven enough the engine is fully warmed up the battery may not receive a full recharge. A modern car has big electrical loads and to satisfy these means the battery may not get all the electricity it needs from the alternator as these other electrical loads get their share. This is more likely if the car is driven around town with low engine RPMs as the alternator output is lower at low RPMs.

Roughly with my 996 (thanks to its dash resident volt meter) I can say it takes around 10 to 15 miles or so of steady driving to top up the battery. This is during daylight with no extra electrical loads. Turn on the auto climate control and headlights and it can take even longer.

Awesome charging potential, relatively low electrical loads.

Grant

Grant

gee-lenahan-at-gee-mail-dot-com

A 40 mile one way drive even with just 2/3rd highway certainly seems sufficient.

A bit of grasping at straws here, but are you sure that drive was non-stop? No stopping for a coffee and pastry? What about once at work? No short run at noon for a lunch? Every engine start takes its toll.

There is too the possibility the battery was just bad. I recall the battery that came with my used 996 didn't last very long. I did not know its age or how it was used, but replaced the battery with a new one just like it, properly sized but not a factory (Moll) battery, but an Interstate battery. 7 months later the new battery was dead. Nothing to do with how I drove the car as I drove the car the same way day in and day out and normally get very good battery life. Just a crummy battery out of the box.

Its just the instant failure that was weird.

No stops. No noon runs. That's my point, its pretty much impossible to treat the battery better than it had been the previous week before death.

I suspect a cell shorted, but, as i noted way back up top, this is where my chemistry comes up lacking. If it was still, dead at 12.3V no-load, "short" is not quite the right term. Its more like "near-infinite output impedance suddenly due to some mechanical failure", which i'm perfectly willing to accept, but i'm also aware that i don't truly know what occurs or how to either identify it or prevent it.

All water under the bridge now, since i have a new AGM battery in it.

Interesting note: the AGM is 58.5 lbs. The identical slosh-type, same brand, etc is 46 lbs. I didnt realize that when i bought it.
I did when i lifted it though, especially up and over a big v8, arms out, and into a teeny-tiny opening behind the firewall.

Grant

Grant

gee-lenahan-at-gee-mail-dot-com

We know the battery failed for some reason.

Sulfation
Sulfation is always present to some degree in any lead-acid battery, more so in a battery with usage patterns like yours
Since the charging system can be fooled into not charging a sulfated battery correctly, it is entirely possible that one day the charger suddenly becomes ineffective
A heavily sulfated battery with no recharge will die very quickly

Normal wear because of battery age
A non-sulfated battery that just wears out over time loses its ability to hold a charge very gradually
The symptoms you describe are less likely to be a result of battery age

Other causes
Battery technology is pretty simple and the number of common causes of failure is very small (essentially just these two)

Addressing a sulfated battery is quick, easy, and cheap, which is why I recommended it.

remember the horse is long out of the barn.

But i simply don't understand your logic here.

everything i know and read says my pattern does NOT fall into that for sulfation. From what i read, that would be common with a battery that sits for long periods unused. A fully charged battery is not a good candidate for sulfation. Mine is used regularly, aside from frequent business trips.

That said it is almost NEVER low on charge, from any day-to-day observation. Even in subfreezing weather it always cranked like a champ.

What about my usage pattern leads to sulfation.

For me, BTW, it would have been neither a quick nor easy fix, as i understand it. One needs to buy a battery tender (or similar) to do so.

Easier way? I bet an other battery of mine WAS sulfated and might have been saved, so it would be good to know if there is a non-dedicated equipment route.

Grant

Grant

gee-lenahan-at-gee-mail-dot-com

implies that you did that more than once. That exacerbates sulfation. Additionally, your battery is 8 years old and sulfation accumulates over time. A moderately sulfated battery will still start a car in freezing weather without issue. A battery that reaches the point of sulfation where the charger stops charging it (or worse intermittently charges it) will stop functioning very quickly.

Your horse is out of your barn but remember that this forum is not just here to help people as they ask questions but to serve as a source of information for people who have problems and are searching the web for help. That's why it's valuable to discuss and understand the cause of problems even after the problem has been "replaced away".

My above point was that however improbable you think sulfation is, normal battery wear or some rare battery issue are both less likely.

To solve the sulfation problem you either buy or borrow a desulfating charger. Or you take the battery (with or without the car) to someone who has one. I'm guessing that most auto parts stores will do this for you for free. And probably most auto repair shops too, worst for a nominal fee.

"implies that you did that more than once."

Oh yes, it will sit 2 weeks 10-20 x/yr and still does. But it is always strong at the end of the two weeks and gets a LONG run regularly - 30-100 miles regularly.

But i guess you are saying that will do it, with no intervening symptoms ( the part i frankly find hard to accept)

"Your horse is out of your barn but remember that this forum is not just here to help people as they ask questions but to serve as a source of information for people who have problems and are searching the web for help."

Yep, agree. That's why i want the fuzziness removed - for all and for me in the future. I still find it fuzzy, by the way. A situation that incrementally causes a battery to not take charge shoudl result is a slowly dying battery, not one that cranks like a champ in zero degree weather after a two week sit. Still nto adding up for me.

"To solve the sulfation problem you either buy or borrow a desulfating charger."

yea, that's the rub. I looked in the fridge and it wasn't there. Nor did the two local shops i tried, and traveling is simply not worth it for an old battery that wont live long anyway. The more i hear, the less i think its much pf a practical solution - more of a curiosity to know what happened.

If i can simply make all my batteries last 8+ years i'll be thrilled. Hint: leave them for two weeks regularly :-) Just reading the facts, i cant exp[lain it either.

Grant

Grant

gee-lenahan-at-gee-mail-dot-com



Edited 1 time(s). Last edit at 10/13/2014 07:46PM by grant. (view changes)

some kind of internal mechanical failure that caused probably several plates to short or ground or whatever it is plates can do (wrong) inside the battery case.

Grant

gee-lenahan-at-gee-mail-dot-com