Question: what is the difference between a 3 cell and 4 cell battery?
Answer: I've no experience with this notebook but the 3 cell battery is 37Whr and the 4 cell is 55 Whr so it has about 50% more capacity. Which, for a given usage pattern, means 50% more run time. Personally, for 105g (about 4 ounces) extra weight I wouldn't hesitate to get the bigger battery.