To give closure, alternator replacement appears to have cured my issues. Battery and brake warning lights now illuminate at key on and shut off after engine start. Reading 14.4vdc @ idle after the GP relays click off.

Curiously, after charging the battery and parking the car for a couple of days while I awaited a new alt, the battery discharged again. Now I had the old bad alt hooked up still so perhaps it had some internal fault (short) that drained the battery. Well, that's what I'm gonna tell myself for now. With everything all repaired now and the key off and battery discon I see no voltage drop upon connecting the battery, so I don't think I have a parasitic draw anywhere.

About the LED headlights, they're plug and play 7-inch round units manufactured by Truck-Lite. They're very low draw, probably less than the brake lights, however they're not tolerant of voltage drops, so the internal circuitry will cut them out once levels drop below tolerance.

The rest of the car is stock, except LED dome lights and license plate lights. I'd do the marker lights but the LED units I've found don't seem to play well in the housings, resulting in poor illumination/visibility. Same with the brake and tail lights. The signal lights are similarly a no-no and have the added problem of screwing up signal operation, as the draw isn't enough to operate the flasher units. To correct this one must wire a resistor in line, which defeats one of the major advantages of LED, which is low power draw.

The radio is all stock.

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Own:
1970 Mercedes 250c, 1976 International Scout II, 1982 Mercedes 240d, 1997 Honda Accord Wagon, 1998 Acura Integra Type-R, 2009 Mazda5.
Owned:
1974 International 100 pickup, 1975 International Scout II, 1981 Mercedes 240d, 1985 Mercedes 300SD, 1988 Honda Accord, 1988 Ford Thunderbird, 1991 Honda Accord, 1996 Geo Metro, 1996 Ford F150, 1996 Dodge Grand Caravan, 1997 Honda Accord, 2003 Acura TL-S, 2003 Yamaha V-star.