you might find answers to this in your reference booklet, or via the apple tech support website. keep in mind that what they advertise is rarely “accurate” in the truest sense. Laptops are tested with WiFi off, no music playing and with 20% screen brighness. Not how we typically run our laptops. my old powerbook (before the battery died) got maybe 2.5hrs out of the battery, with normal usage. my new macbook pro, which is advertised at 7, gets 3–3.5 with normal usage (though i do have it autodim the screen a bit when unplugged).