Whoa, hold on here... don't run away with my thread here guys!

It is not common for computer controlled cars to run 15 volts. Just because there are a lot of accessories on board, does not mean it needs more voltage to run. Voltage =/= capacity. Current = capacity. Hence the threads about bigger capacity alternators to run cars with a big stereo system. I only have the 105 amp alternator, but might try to get a 140 if it will fit.
Electrical load like lights, heating elements, etc, are rated to perform under a wide range of voltage. But they work as designed under a narrow range.


I've had my share of computer controlled cars. Even dating back to my 87 Regal. It has a 3.8L turbo, and has never seen voltage top out above 14.6. It had a system in it, with one regulated power amp for mids/highs, and an unregulated amp for the subs. Just about every piece of wire in that car has passed through my hands, down to the wiring for the custom fan, and 8 gauge fuel pump feed and ground.
I have my dads Subaru Forester out here, with power moonroof, rear defrost, heated seats, foglights, front defrost, heated wipers, heated washer fluid, etc etc. I bet you it isn't running at 15v. I know my 01 Cruiser parked out here, with custom LEDs, reverse lights, stereo setup, moonroof, heated seats and foglights, etc etc has never seen voltage that high, even on a nearly dead battery that needed a jump. My sisters 00 Regal LSE doesn't see 15v either. Its running a stock 3800, with power roof, seat heaters, stereo, digital climate control, etc etc. It still has all original switches, no dash bulbs or switch backlights are out. Seat heaters work great. Hasn't needed a new tail or headlight bulb in the last 2 years, and she used to drive 3 hours a day or more with it.
15V may be a normal at the "extreme" ends of the charging spectrum (for very short periods of time), but 15V all the time is not.

thats what i was tryng to say, the charging at speed when your rpms are 2Kish can be 14.5 give or take a couple tenths but thats a best case, i always test at capacity which is what matters like jason said, turn everything on at idle and check the battery voltage with a real meter because the one on the dash is usually only accurate enough to give you an indication of a problem. if you have 13.7 give or take a few tenths after the battery has charged from starting the engine than the alt is fine.

you test your battery by testing the voltage when you are starting it, and or listening to the car when it starts. as long as the terminals are maintained thats really all you need to do.

I know my car dash digital display on voltage is low by 1.1 volts. So I just add 1 as I know from using the VOM connected to batt terminals is accurate. If you are always at 15v and no variance what so ever, that is a problem with the regulator or weak battery? I am not sure anymore with all the new cars with PCM, if the GM alt even has an internal regulator or not.
In the am when I start the car the voltage output is highest 14.8-15v for about 15 minutes while the battery gets charged up, then drops back to about 14.3v.
There should be some variable voltage happening.

I have been watching my volt meter for the past few days since you started this post. The lowest that I have seen my volt gauge at was 14.6v. The normal is 15v and sometimes it is 15.1v. It would be interesting to see how many volts other peoples cars are putting out. You can try replacing your alternator and ECM and see if that will bring you down .5v but I don't think it is worth the money or effort. Either 14.6 - 15.1 is normal or my car has the same problem.

check your voltage with a meter and see if its even the right reading.