AudiForums.com - Battery not holding charge, Alternator warning indicator not showing.

Hi all.

This is my first post on this forum, so I am hopeful for a warm reception, as I am no expert by any means. I am however, having fun undertaking more and more DIY and the information I have found here has been extremely helpful and appreciated.

This week my CEL appeared on my '03 A4 1.8T, and I didn't feel comfortable driving the car from where I was, so I arranged for a tow and was able to get it back in my garage. Fortunately, I had just picked up an ODBC scanner, and pulled Ignition Coil and Spark plug repair codes. Through other transportation, I picked up the coils and plugs and, replaced everything pretty easily within 30 minutes, then erased the codes with the scanner before restarting to check my work. Here is the weird part. The car wouldn't start. Just the clicking sound from a dead battery. Using a 500amp portable power station, the car fired right up. I let it run for about 10 minutes, then shut it off. :45 minutes later, I restarted the car, The CEL light was gone, but the ESP light was now on. At first the car seems to run fine, again no engine light, but again the ESP light is on, then the RPMs drop to <1000 and the idle gets rough, and the lights flicker as though the car is losing electrical juice, and about to stall out. I naturally start to think this is symptomatic of a dying Alternator, but that warning indicator does not pop up.

The timing is odd that this occurs immediate after replacing coils & plugs , or it is just extremely coincidental. In any case, the battery is a 5 y/o AAA battery and that will be replaced. I am raw with respect to trouble shooting anything electrical but I am picking up a multi-meter this afternoon. Any guidance on how best to trouble shoot the cause?

Thanks a ton for any advice.