Chonic Alternator Failure
I worked as a service writer for a dealership for a couple of years out of college. Many times we would get older cars (say 5 or so years old) that would have a bad alternator. After pricing the dealer item, then the better aftermarket rebuild, many would INSIST that we install an AUTOZONE alternator. All the mechanics would cringe and we had a policy to explain that even though they had a free replacement at AZ, that we would not honor any sort of labor warranty. We knew from past experience that you could go through 4 or 5 alternators (or starters) before you found one that would work more than a couple of days. There reputation for electrical items was really really bad. It was always the local NAPA or CAR QUEST that we used for aftermarket rebuilds. It made a big difference. On the same note, I was reading through this discussion and didn't see any note about what type, age, and size of the battery you use. Also, are there any accessories installed (amplifiers, A/C, lighting upgrades) that would really stress the factory system? Have you looked at your alternator and battery ground or you battery cable conditions? How about coil condition? How is your main feed at the firewall bulkhead? Burnt connections or poor conductivity? What type/brand of voltage regulator are you using? Switch brands? I would agree that a weak or bad battery could really put a hurting on your system. Having discharge at idle with the lights on is common and almost considered normal especially if you have replaced your headlamps with halogen or any other sort of higher wattage bulb. That is why you see many converting over to relay systems. Personally, I went through my entire charging system by using a PowerMaster alternator, relay added for the run circuit, additional heavy charging wire from alternator to to starter relay, headlight relay system with heavier feeds to headlights, and a decent heavier capacity battery that is kept on a maintainer when not in use. Even with all that, a lot of stop and go driving with the stereo going, headlamps on, and/or the heater/AC fan running will give a discharge condition at idle since more power is being required than that charging system can provide at the lower rpm. Also, avoid the "blue" race-only voltage regulators. They are designed for short term use and create an overcharging condition that can fry a battery or old wiring in a heartbeat. Hope some of this helps.