Hi David ....
I tried the coin battery hack on an A2000 rev 4.5 MoBo.
It didn't work ... I tried with 2 different NEW batteries.
What I found on the A2k is it needs the extra point 6 volts
to hold the time/date. I posted this results on A.Org here
awhile back. There was a few comments from others that have
done the hack with varying degrees of success from "Didn't
work" to "holds time for awhile".
I'd say try it, if it works 'Great', if not, add another
battery. (I din't think you would hert anything by having
4.5 volts. I'm sure someone will correct me if I'm wrong)