Charging issue on startup

'96 F250, 7.3L PSD.

On initial startup, the voltmeter in the cab reads low - maybe at 1/4 of the gauge. I haven't put an actual voltmeter on the batter yet, so I'm not sure the exact voltage. The charge light on the dash will come on sometimes but not always. If you tap the accelerator, the voltage goes up but falls back at idle. Once you drive the truck - and mean even 500 feet - it comes up to just above half way on the gauge and stays there, even at idle. Once driving, it seems great.

Batteries are new. Changed the serpentine belt too - I thought it might just be slipping when cold. I noticed some slight sandy noises when rotating the alternator with the belt off. Regulator is built into the alternator on this one, btw.

So...Any guesses? New alternator needed or some other weirdness going on?

Double check the cleanliness of the battery and Alt connections. sounds like weak connection or the start of failing brushes.

I'll double check them but the one battery I've had out had great connections.

The guys on the diesel forum tell me that the glow plugs stay on for up to 2 minutes and draw a LOT of power. They're saying that it's normal on these trucks to see that on the voltmeter. Sounds reasonable, I guess....

Battery voltage is one thing. since it starts the engine, can't be too low.

Alternator charging voltage is another. At app. 1500 rpm it should be charging 14.3+- volts.

Random charge indicator light indicates a malfunction.