Increasing battery working time on Lenovo W500

I'm a happy user of a Lenovo W500 but I had a very hard time getting anything more than 1h30 battery time, even with a brand new 9-cell battery (this one got me just 1h45 when using low screen brightness and minimum CPU). Then through a conversation with a friend and colleague, he suggested I disable the ATI graphics card and use the motherboard's... This means disabling it in the system's BIOS (not inside whatever operating system you use). Since I tried that, I get up to 4h45 on my 9-cell (with the minimum energy usage configuration in Ubuntu 10.10 64bit).
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