My 2002 VW New Beetle has a sketchy (dis)charging issue. Specifically it appears that while the AC is running (though I'm not positive that's always the case) after about 15-20 minutes of driving the battery discharges enough that the engine/car goes all herky jerky and eventually the motor stalls out.
We suspected the alternator was the issue - O'Reilly's machine says it's producing enough juice to keep things going. With the engine off, measuring voltage across the terminals gives 12.9v. I thought there might be a parasitic draw, but if there is it's not a consistent one. I had it charged over a week ago, and it started OK today. I suspected the battery (Energizer, bought at Sam's Club) but they said it tested OK and just had a low charge.
I have a cheap-o amazon battery tester, and after topping it up last week I turned the headlights on for about 10-20s, hooked up the tester and it said the 650 CCA were fine.
The last day things went unfortunate -- a week ago Sunday -- I had driven 13 miles, about 20 minutes, mostly on the Interstate when it died on me. The engine was running but there was no throttle response at first, and then I jerked into a parking lot. From there I was able to jump start it with a jump pack and made it all of 20 feet before the engine lost power (though it was still running). I only had about a mile left to go so crossing my fingers, I wedged the jump pack in and left it hooked up and managed to get to my destination.
Later that day to get it back, I had my partner jump the car -- we left it hooked up for about 5-10m and then I took off again. I managed about 5 miles before the car... well, honestly it acts like it ran out of gas, but it's something with the electrical. Jumped the car again, left it hooked up for about 5 minutes, and made it about another 5 miles. Wash, rinse, repeat 2x and I was able to make it home.
To review the facts:
- battery takes a charge, will hold it for over a week at >12v
- after a full charge, turning headlights on for ~10-20s, the battery tested fine at 650 CCA
- O'Reilly's alternator tester says it provides enough juice
- Testing across the terminals while the engine is running reports ~13V. 12.9-13V. Definitely not 14+. Turning the AC on full blast doesn't appear to have a significant impact (maybe 0.1v?)
- Jump starting will allow the car to run for a short period of time
- When the battery voltage (?) gets low enough the car acts like it's out of gas.
What other tests can I run to figure out what's going on here? I have read that some of the wiring in the box on top of the battery is a bit undersized -- there's some evidence that one of the wires (black, furthest to the left) may have been a bit toasty at one point in its life. It's not completely burnt, but the metal is not shiny, and the jacket looks like it's been cooked.
What can I do to further track down this issue?