Both the backup battery and the main battery are working fine. Problem
is, when the backup battery is powering the bios, the machine won't
power on, even if connected to AC power (as I say, I suspect the power
management is too blame).

Without the backup battery, it powers on, but the system keeps cycling
to back to the BIOS and asking me to set the time. If I could be done
with the backup battery altogether that would be great, but I can't
seem to get past the BIOS without it installed.