I have an S6410 and recently switched to Windows 7. I have noticed that my battery does not last as long as it used to, but the change was not as dramatic as you report. I had also been having serious problems with Vista SP2, so I have not changed back.
In any event, I think that you do not have the latest BIOS. You should have version 1.31 published by Fujitsu and Phoenix in May 2009.
I find the Fujitsu web sites and help information confusing and lacking, so I tend to trawl around for as much information as I can get. I am British and live in Asia, but I only found this BIOS, and a step by step guide to loading Windows 7 on the Fujitsu US web site - even then the upgrade failed several times and I twice had to call Microsoft for technical help.