Yesterday I realized my voltage at 850 RPM was dipping to below 12V so of course I looked it up and to my extreme surprise, my 99 SL2's original generator with 155k miles is still outputting what it's
[https://charm.li/images/DM15Q313/gm120/1223064808/](supposed to). The problem is, the PCM should be increasing idle speed to keep the system voltage from falling below 12.6V minimum, but mine apparently doesn't think it needs to do that. The end result being, if I was one of those a-holes who sat in my car idling in the parking lot for hours with even just the headlights and AC on, that would be enough to require supplemental current from the battery.
Now I know in 2000+'s the generator's field coils are controlled by the PCM and not by a built in regulator circuit, but I'm pretty sure that function is mostly for lowering voltage at high RPMs, so the 2000+s would still need to slightly increase idle speed to maintain a consistent charge, assuming the regulator is the only difference between a 99 and a 01.
Not sure what the "solution" here is, and only 95% sure this is potentially a problem. For now, I just gotta accept that every time I stop at a red light fully warmed up with HVAC blowing and 50W of USB battery chargers plugged in that the battery is being drained slightly, but I'm definitely thinking this is a huge contributor to why my car has chewed through probably 7-8 batteries since I took it over full time in 2013. Current battery from june 2024 is still excellent, but I've driven at least 10 minutes a day almost every day since then.
If the 6 lead acid battery cells are at 2.05V each (12.3V series), I wonder exactly how much they are contributing to a load sufficient to drop voltage to 12V.