Absolutely MUST install via Battery - Help please?

Hello, Im currently running Vista Ultimate Beta Edition. My Beta will run out
in about 9 days.

I bought Windows Vista Business Edition at my bookstore. (for 75$ because of
the microsft student discount)

It wont let upgrade when booting from the disc, instead wants to do a clean
install.

When installing from within vista, it warns me that I cannot install via
battery.

My Sony VAIO notebook has a glitchy power port, and does not make a good
connection so the battery indicator is always flashing from plugged in to not
plugged in (constantly)

it appears impossible for me to get a solid enough "plugged in" signal to
the computer to let vista install.

When installing from Battery power it should be fine (I have 3 hours of
battery life on High settings) but it wont let. me.

Ther HAS to be some sort of command line extension that will let me install
it from battery.

My other guess would be to backup the data, and do a clean install via the
boot from CD option.

Please help. After the 9 days are up my computer will be useless.