I have a brand new. I have a brand new Lenovo R61, but the battery doesn't last for more than 1.5

Question

I have a brand new Lenovo R61, but the battery doesn't last for more than 1.5 hrs even after a full charge. The spec says it should last at least 3.5 hrs. They sent me a new one but it's performing the same. I'm mostly watching downloaded video clips and surfing the web only and they should not be unusually power sucking (or so unusual that the spec'ing environment they used would be drastically different)Could it be that there's a "power eating" setting I have accidentally set? How can I extend the battery's life to what it says on the spec?