Sorry, I can't help you as I don't have that problem with my Gateway
Laptop. I had 9.04, 9.10 and now 10.04 on it and when the power plug
is disconnected it sounds a chime and reports in the lower right
corner that the power has been disconnected. On reconnection it
reports that and carries on as usual. I think that is the way it is
supposed to work but some hardware is a bit fussier.

Have you tried an internet search to see if anyone else has that
problem with your make and model?