Just an update on this topic:
After my little voltmeter told me my PSU was consistently putting out only 18.5VDC rather than its specified 19.5V (over 5% below spec), I decided to take a $60 gamble and buy a new power supply. Dell no longer carries this model, so I had to go to the Internet and find a third-party vendor reselling original Dell parts.
The good folks at AtBatt.com had my original 150W adapter for $60 total - brand new, not refurbished - and it has completely olved my problem. No more POST messages, my battery charges properly, heck, even my iced tea tastes better now. :)
Thanks to those who offered suggestions here.
My Inspiron 9100 started to give me the same message after updating software for portabele computers, you car turn the check for AC-adaptertype "OFF" in bios settings, then you w'ont get this message at every boot. My battery works fine, and is properly charged.