maytag

Hey y'all:
I bought an '00 TT 1.8T several months ago. I drove it a few times over a couple weeks, and then parked it while the weather was unbearable.
Last night I went to start it and the battery was COMPLETELY dead. I could not measure ANYTHNG (I thought my meter was bad!)
Battery Charger has been on the battery for over 24 hours now, and it's weird: still not measuring anything. SO I hooked-up jumper cables to my jeep. I've got 14.5v at the cables, until I attach 'em to the battery, at which time it drops to nearly 0 (like, 0.01v). But randomly it jumps to 12.5v and I can operate something in the car for a MOMENT, and then it drops back to ZERO.

So: I pulled the battery. The battery is now accepting a charge just fine. Slowly, but it's coming up as I would expect. However, when I attach the jumper cables from the JEEP to the cables in the car, again, drop to ZERO at the cables.

I'm suspicious of a short to ground. it's very weird. I'm thinking voltage regulator.

any suggestions? IS there a way to test my theory?

HELP?

Redd

If there was a dead short in the TT, when you attached the Jeep cables there would be fireworks from the short. So whatever is bad, is probably more complicated than that.

Could be a broken contact in the battery, an intermittent flaw that's opening and closing from vibration and temperature. Could be a problem in the car.

If you're brave and it fits...you can eliminate that possibility by putting the TT battery in the Jeep for a week and watching the voltage.

Otherwise I'd start with the wiring from the alternator to the battery and starter in the TT, look for anything loose or corroded. Those are your primary power wires, but there's miles of other wiring that can problematic, you'd have to start pulling fuses to isolate circuits, and check out systems till you could find the fault.

But I'm still thinking, you have an internal failure in the battery, if you're lucky.

maytag

Thanks for the speedy reply! I appreciate your assistance. We'll see how the battery tests tomorrow. But I really do not believe this to be a battery issue,because of what I described in the last paragraph of my post. I can think of no reason that attaching jumper cables that read 14.5 volts to the cables of the car should result in no voltage. It makes no sense to me.
But I'm planning to do as you say tomorrow and start with a fresh battery. We'll see what we can learn at that point.
(Oh, and bravery is never something I'm short on... usually my failure to truly comprehend the risk is my bigger hurdle... haha)

Redd

Speaking of bravery (or paranoia) there are some 10,000 accidents per year, just in the US, where people are blinded or hospitalized for eye damage from exploding batteries, usually while jump starting.

Just in case there's something really odd going on...I must admit I usually don't use the $3? $5? goggles that came with my cables, or the ones with my power tools, but you might think about that.

If your cables are good, and your jeep was running, you would still see 14.5V on the Audi at the point where the cables went. Cables rarely go bad but sometimes they just don't bite into the battery posts and "zero" means they really aren't connected.

There are also battery primary fuses in cars these days, I'd expect you 2000 model to have one. If the inconspicuous wire from the Audi battery to a primary fuse (usually located within one foot of the battery, could be in either lead) was loose, corroded, or that fuse failing, that would be another primary point to check. Another thing that's so simple and obvious, we never look at it.

mister pepper

It's been a week and the car has started every time. I even left it sitting for 2 days straight without issue. It's looking like I may have figured out the problem. I'll keep the amp unplugged for another week just to be sure. In the meantime I may open it up to see how repairable it is for a layman like me.