FEY42
6 Indium

RE: 5748 will not turn on without battery.

It was the adapter. The two I had were the right voltage and working fine, but were not Dell compatible. i.e they were missing the reply signal thru the third pin.

The new Dell adapter reports back and the BIOS shows "90W"

It now boots from just the adapter and charges both the old and new batteries.

Problem solved, I can now sell this thing and walk away.