Although the increase in battery runtime - 13 minutes when going to 4 GB - doesn’t look like a big deal in the context of seven hours of battery runtime, such an upgrade is still worth it. On the one hand, the cost for a 4 GB kit has dropped below $100, making such an upgrade extremely affordable. On the other hand, the memory upgrade will both increase battery runtime and your system responsiveness, as well as application performance when multiple programs are being executed. Finally, a memory upgrade often can be performed with little effort, as all parts of a notebook can usually be accessed easily.
If you decide to upgrade from 1 GB to 2 GB you’ll not experience a lot of battery runtime benefits, as the more significant step is made with the upgrade from 2 GB to 4 GB. Obviously, Windows Vista Ultimate (which cannot utilize more than 3573 MB in the 32-bit version) effectively reduces page file swapping on the hard drive and may also involve Vista’s SuperFetch buffering feature more aggressively. However, most of the battery runtime gains can be attributed to the reduced swapping activity, as the 7,200 RPM Hitachi TravelStar hard drive requires several watts of power when active.